Av(1324, 1342, 2341, 2431)
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Generating Function
\(\displaystyle -\frac{x^{5}+14 x^{4}-31 x^{3}+24 x^{2}-8 x +1}{\left(x^{2}-3 x +1\right) \left(2 x -1\right)^{3}}\)
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Counting Sequence
1, 1, 2, 6, 20, 67, 219, 694, 2135, 6399, 18758, 53971, 152883, 427462, 1182239, ...
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Implicit Equation for the Generating Function
\(\displaystyle \left(x^{2}-3 x +1\right) \left(2 x -1\right)^{3} F \! \left(x \right)+x^{5}+14 x^{4}-31 x^{3}+24 x^{2}-8 x +1 = 0\)
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Recurrence
\(\displaystyle a \! \left(0\right) = 1\)
\(\displaystyle a \! \left(1\right) = 1\)
\(\displaystyle a \! \left(2\right) = 2\)
\(\displaystyle a \! \left(3\right) = 6\)
\(\displaystyle a \! \left(4\right) = 20\)
\(\displaystyle a \! \left(5\right) = 67\)
\(\displaystyle a \! \left(n +5\right) = 8 a \! \left(n \right)-36 a \! \left(n +1\right)+50 a \! \left(n +2\right)-31 a \! \left(n +3\right)+9 a \! \left(n +4\right), \quad n \geq 6\)
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Explicit Closed Form
\(\displaystyle \left\{\begin{array}{cc}1 & n =0 \\ \frac{\left(24 \sqrt{5}+120\right) \left(\frac{3}{2}-\frac{\sqrt{5}}{2}\right)^{-n}}{80}+\frac{\left(-24 \sqrt{5}+120\right) \left(\frac{3}{2}+\frac{\sqrt{5}}{2}\right)^{-n}}{80}-\\\frac{2^{n} \left(n^{2}+9 n +30\right)}{16} & \text{otherwise} \end{array}\right.\)
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This specification was found using the strategy pack "Point Placements" and has 123 rules.

Found on July 23, 2021.

Finding the specification took 5 seconds.

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\(\begin{align*} F_{0}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{2}\! \left(x \right)\\ F_{1}\! \left(x \right) &= 1\\ F_{2}\! \left(x \right) &= F_{3}\! \left(x \right)\\ F_{3}\! \left(x \right) &= F_{18}\! \left(x \right) F_{4}\! \left(x \right)\\ F_{4}\! \left(x \right) &= F_{0}\! \left(x \right)+F_{5}\! \left(x \right)\\ F_{5}\! \left(x \right) &= F_{6}\! \left(x \right)\\ F_{6}\! \left(x \right) &= F_{18}\! \left(x \right) F_{7}\! \left(x \right)\\ F_{7}\! \left(x \right) &= F_{120}\! \left(x \right)+F_{8}\! \left(x \right)\\ F_{8}\! \left(x \right) &= F_{4}\! \left(x \right)+F_{9}\! \left(x \right)\\ F_{9}\! \left(x \right) &= F_{10}\! \left(x \right) F_{115}\! \left(x \right)\\ F_{10}\! \left(x \right) &= F_{11}\! \left(x \right)+F_{46}\! \left(x \right)\\ F_{11}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{12}\! \left(x \right)\\ F_{12}\! \left(x \right) &= F_{13}\! \left(x \right)\\ F_{13}\! \left(x \right) &= F_{14}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{14}\! \left(x \right) &= F_{15}\! \left(x \right)+F_{19}\! \left(x \right)\\ F_{15}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{16}\! \left(x \right)\\ F_{16}\! \left(x \right) &= F_{17}\! \left(x \right)\\ F_{17}\! \left(x \right) &= F_{15}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{18}\! \left(x \right) &= x\\ F_{19}\! \left(x \right) &= F_{20}\! \left(x \right)+F_{32}\! \left(x \right)\\ F_{20}\! \left(x \right) &= F_{21}\! \left(x \right)\\ F_{21}\! \left(x \right) &= F_{18}\! \left(x \right) F_{22}\! \left(x \right)\\ F_{22}\! \left(x \right) &= F_{23}\! \left(x \right)+F_{24}\! \left(x \right)\\ F_{23}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{18}\! \left(x \right)\\ F_{24}\! \left(x \right) &= F_{20}\! \left(x \right)+F_{25}\! \left(x \right)\\ F_{25}\! \left(x \right) &= F_{26}\! \left(x \right)+F_{27}\! \left(x \right)+F_{31}\! \left(x \right)\\ F_{26}\! \left(x \right) &= 0\\ F_{27}\! \left(x \right) &= F_{18}\! \left(x \right) F_{28}\! \left(x \right)\\ F_{28}\! \left(x \right) &= F_{29}\! \left(x \right)+F_{30}\! \left(x \right)\\ F_{29}\! \left(x \right) &= F_{18}\! \left(x \right)\\ F_{30}\! \left(x \right) &= F_{25}\! \left(x \right)\\ F_{31}\! \left(x \right) &= F_{18}\! \left(x \right) F_{20}\! \left(x \right)\\ F_{32}\! \left(x \right) &= F_{26}\! \left(x \right)+F_{33}\! \left(x \right)+F_{45}\! \left(x \right)\\ F_{33}\! \left(x \right) &= F_{18}\! \left(x \right) F_{34}\! \left(x \right)\\ F_{34}\! \left(x \right) &= F_{35}\! \left(x \right)+F_{38}\! \left(x \right)\\ F_{35}\! \left(x \right) &= F_{16}\! \left(x \right)+F_{36}\! \left(x \right)\\ F_{36}\! \left(x \right) &= F_{37}\! \left(x \right)\\ F_{37}\! \left(x \right) &= F_{16}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{38}\! \left(x \right) &= F_{32}\! \left(x \right)+F_{39}\! \left(x \right)\\ F_{39}\! \left(x \right) &= 2 F_{26}\! \left(x \right)+F_{40}\! \left(x \right)+F_{44}\! \left(x \right)\\ F_{40}\! \left(x \right) &= F_{18}\! \left(x \right) F_{41}\! \left(x \right)\\ F_{41}\! \left(x \right) &= F_{42}\! \left(x \right)+F_{43}\! \left(x \right)\\ F_{42}\! \left(x \right) &= F_{36}\! \left(x \right)\\ F_{43}\! \left(x \right) &= F_{39}\! \left(x \right)\\ F_{44}\! \left(x \right) &= F_{18}\! \left(x \right) F_{32}\! \left(x \right)\\ F_{45}\! \left(x \right) &= F_{18}\! \left(x \right) F_{19}\! \left(x \right)\\ F_{46}\! \left(x \right) &= F_{12}\! \left(x \right)+F_{47}\! \left(x \right)\\ F_{47}\! \left(x \right) &= F_{26}\! \left(x \right)+F_{48}\! \left(x \right)+F_{85}\! \left(x \right)\\ F_{48}\! \left(x \right) &= F_{18}\! \left(x \right) F_{49}\! \left(x \right)\\ F_{49}\! \left(x \right) &= F_{50}\! \left(x \right)+F_{53}\! \left(x \right)\\ F_{50}\! \left(x \right) &= F_{16}\! \left(x \right)+F_{51}\! \left(x \right)\\ F_{51}\! \left(x \right) &= F_{52}\! \left(x \right)\\ F_{52}\! \left(x \right) &= F_{18}\! \left(x \right) F_{50}\! \left(x \right)\\ F_{53}\! \left(x \right) &= F_{54}\! \left(x \right)+F_{71}\! \left(x \right)\\ F_{54}\! \left(x \right) &= F_{26}\! \left(x \right)+F_{55}\! \left(x \right)+F_{63}\! \left(x \right)\\ F_{55}\! \left(x \right) &= F_{18}\! \left(x \right) F_{56}\! \left(x \right)\\ F_{56}\! \left(x \right) &= F_{35}\! \left(x \right)+F_{57}\! \left(x \right)\\ F_{57}\! \left(x \right) &= F_{54}\! \left(x \right)+F_{58}\! \left(x \right)\\ F_{58}\! \left(x \right) &= 2 F_{26}\! \left(x \right)+F_{59}\! \left(x \right)+F_{62}\! \left(x \right)\\ F_{59}\! \left(x \right) &= F_{18}\! \left(x \right) F_{60}\! \left(x \right)\\ F_{60}\! \left(x \right) &= F_{42}\! \left(x \right)+F_{61}\! \left(x \right)\\ F_{61}\! \left(x \right) &= F_{58}\! \left(x \right)\\ F_{62}\! \left(x \right) &= F_{18}\! \left(x \right) F_{54}\! \left(x \right)\\ F_{63}\! \left(x \right) &= F_{18}\! \left(x \right) F_{64}\! \left(x \right)\\ F_{64}\! \left(x \right) &= F_{65}\! \left(x \right)+F_{68}\! \left(x \right)\\ F_{65}\! \left(x \right) &= F_{66}\! \left(x \right)\\ F_{66}\! \left(x \right) &= F_{18}\! \left(x \right) F_{67}\! \left(x \right)\\ F_{67}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{65}\! \left(x \right)\\ F_{68}\! \left(x \right) &= F_{26}\! \left(x \right)+F_{63}\! \left(x \right)+F_{69}\! \left(x \right)\\ F_{69}\! \left(x \right) &= F_{18}\! \left(x \right) F_{70}\! \left(x \right)\\ F_{70}\! \left(x \right) &= F_{16}\! \left(x \right)+F_{68}\! \left(x \right)\\ F_{71}\! \left(x \right) &= 2 F_{26}\! \left(x \right)+F_{72}\! \left(x \right)+F_{84}\! \left(x \right)\\ F_{72}\! \left(x \right) &= F_{18}\! \left(x \right) F_{73}\! \left(x \right)\\ F_{73}\! \left(x \right) &= F_{74}\! \left(x \right)+F_{77}\! \left(x \right)\\ F_{74}\! \left(x \right) &= F_{51}\! \left(x \right)+F_{75}\! \left(x \right)\\ F_{75}\! \left(x \right) &= F_{76}\! \left(x \right)\\ F_{76}\! \left(x \right) &= F_{18}\! \left(x \right) F_{51}\! \left(x \right)\\ F_{77}\! \left(x \right) &= F_{71}\! \left(x \right)+F_{78}\! \left(x \right)\\ F_{78}\! \left(x \right) &= 3 F_{26}\! \left(x \right)+F_{79}\! \left(x \right)+F_{83}\! \left(x \right)\\ F_{79}\! \left(x \right) &= F_{18}\! \left(x \right) F_{80}\! \left(x \right)\\ F_{80}\! \left(x \right) &= F_{81}\! \left(x \right)+F_{82}\! \left(x \right)\\ F_{81}\! \left(x \right) &= F_{75}\! \left(x \right)\\ F_{82}\! \left(x \right) &= F_{78}\! \left(x \right)\\ F_{83}\! \left(x \right) &= F_{18}\! \left(x \right) F_{71}\! \left(x \right)\\ F_{84}\! \left(x \right) &= F_{18}\! \left(x \right) F_{53}\! \left(x \right)\\ F_{85}\! \left(x \right) &= F_{18}\! \left(x \right) F_{86}\! \left(x \right)\\ F_{86}\! \left(x \right) &= F_{64}\! \left(x \right)+F_{87}\! \left(x \right)\\ F_{87}\! \left(x \right) &= F_{101}\! \left(x \right)+F_{88}\! \left(x \right)\\ F_{88}\! \left(x \right) &= F_{89}\! \left(x \right)\\ F_{89}\! \left(x \right) &= F_{18}\! \left(x \right) F_{90}\! \left(x \right)\\ F_{90}\! \left(x \right) &= F_{91}\! \left(x \right)+F_{94}\! \left(x \right)\\ F_{91}\! \left(x \right) &= F_{65}\! \left(x \right)+F_{92}\! \left(x \right)\\ F_{92}\! \left(x \right) &= F_{93}\! \left(x \right)\\ F_{93}\! \left(x \right) &= F_{18}\! \left(x \right) F_{65}\! \left(x \right)\\ F_{94}\! \left(x \right) &= F_{88}\! \left(x \right)+F_{95}\! \left(x \right)\\ F_{95}\! \left(x \right) &= 2 F_{26}\! \left(x \right)+F_{100}\! \left(x \right)+F_{96}\! \left(x \right)\\ F_{96}\! \left(x \right) &= F_{18}\! \left(x \right) F_{97}\! \left(x \right)\\ F_{97}\! \left(x \right) &= F_{98}\! \left(x \right)+F_{99}\! \left(x \right)\\ F_{98}\! \left(x \right) &= F_{92}\! \left(x \right)\\ F_{99}\! \left(x \right) &= F_{95}\! \left(x \right)\\ F_{100}\! \left(x \right) &= F_{18}\! \left(x \right) F_{88}\! \left(x \right)\\ F_{101}\! \left(x \right) &= 2 F_{26}\! \left(x \right)+F_{102}\! \left(x \right)+F_{114}\! \left(x \right)\\ F_{102}\! \left(x \right) &= F_{103}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{103}\! \left(x \right) &= F_{104}\! \left(x \right)+F_{107}\! \left(x \right)\\ F_{104}\! \left(x \right) &= F_{105}\! \left(x \right)+F_{68}\! \left(x \right)\\ F_{105}\! \left(x \right) &= F_{106}\! \left(x \right)\\ F_{106}\! \left(x \right) &= F_{18}\! \left(x \right) F_{68}\! \left(x \right)\\ F_{107}\! \left(x \right) &= F_{101}\! \left(x \right)+F_{108}\! \left(x \right)\\ F_{108}\! \left(x \right) &= 3 F_{26}\! \left(x \right)+F_{109}\! \left(x \right)+F_{113}\! \left(x \right)\\ F_{109}\! \left(x \right) &= F_{110}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{110}\! \left(x \right) &= F_{111}\! \left(x \right)+F_{112}\! \left(x \right)\\ F_{111}\! \left(x \right) &= F_{105}\! \left(x \right)\\ F_{112}\! \left(x \right) &= F_{108}\! \left(x \right)\\ F_{113}\! \left(x \right) &= F_{101}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{114}\! \left(x \right) &= F_{18}\! \left(x \right) F_{87}\! \left(x \right)\\ F_{115}\! \left(x \right) &= F_{116}\! \left(x \right)\\ F_{116}\! \left(x \right) &= F_{117}\! \left(x \right) F_{18}\! \left(x \right)\\ F_{117}\! \left(x \right) &= F_{118}\! \left(x \right)+F_{119}\! \left(x \right)\\ F_{118}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{115}\! \left(x \right)\\ F_{119}\! \left(x \right) &= F_{115}\! \left(x \right)\\ F_{120}\! \left(x \right) &= F_{118}\! \left(x \right) F_{121}\! \left(x \right)\\ F_{121}\! \left(x \right) &= F_{12}\! \left(x \right)+F_{122}\! \left(x \right)\\ F_{122}\! \left(x \right) &= F_{12}\! \left(x \right) F_{65}\! \left(x \right)\\ \end{align*}\)