Av(1342, 1423, 2341, 3241)
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Generating Function
\(\displaystyle -\frac{2 x^{3}-4 x^{2}+4 x -1}{x^{4}-5 x^{3}+7 x^{2}-5 x +1}\)
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Counting Sequence
1, 1, 2, 6, 20, 67, 223, 740, 2454, 8138, 26989, 89509, 296858, 984534, 3265220, ...
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Implicit Equation for the Generating Function
\(\displaystyle \left(x^{4}-5 x^{3}+7 x^{2}-5 x +1\right) F \! \left(x \right)+2 x^{3}-4 x^{2}+4 x -1 = 0\)
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Recurrence
\(\displaystyle a \! \left(0\right) = 1\)
\(\displaystyle a \! \left(1\right) = 1\)
\(\displaystyle a \! \left(2\right) = 2\)
\(\displaystyle a \! \left(3\right) = 6\)
\(\displaystyle a \! \left(n +4\right) = -a \! \left(n \right)+5 a \! \left(n +1\right)-7 a \! \left(n +2\right)+5 a \! \left(n +3\right), \quad n \geq 4\)
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Explicit Closed Form
\(\displaystyle \frac{11 \left(\left(\left(\left(\mathrm{I} \sqrt{5}-\frac{15 \,\mathrm{I}}{11}\right) \sqrt{-70+50 \sqrt{5}}+\frac{190 \sqrt{5}}{11}-\frac{570}{11}\right) \sqrt{14+10 \sqrt{5}}+\left(-\frac{84 \,\mathrm{I} \sqrt{5}}{11}+\frac{80 \,\mathrm{I}}{11}\right) \sqrt{-70+50 \sqrt{5}}-\frac{1140 \sqrt{5}}{11}+380\right) \left(\frac{5}{4}-\frac{\sqrt{5}}{4}-\frac{\mathrm{I} \sqrt{-14+10 \sqrt{5}}}{4}\right)^{-n}+\left(\left(\left(-\mathrm{I} \sqrt{5}+\frac{15 \,\mathrm{I}}{11}\right) \sqrt{-70+50 \sqrt{5}}+\frac{190 \sqrt{5}}{11}-\frac{570}{11}\right) \sqrt{14+10 \sqrt{5}}+\left(\frac{84 \,\mathrm{I} \sqrt{5}}{11}-\frac{80 \,\mathrm{I}}{11}\right) \sqrt{-70+50 \sqrt{5}}-\frac{1140 \sqrt{5}}{11}+380\right) \left(\frac{5}{4}-\frac{\sqrt{5}}{4}+\frac{\mathrm{I} \sqrt{-14+10 \sqrt{5}}}{4}\right)^{-n}+\left(\frac{760 \sqrt{5}}{11}-\frac{760 \sqrt{14+10 \sqrt{5}}}{11}+\frac{3800}{11}\right) \left(\frac{5}{4}+\frac{\sqrt{5}}{4}-\frac{\sqrt{14+10 \sqrt{5}}}{4}\right)^{-n}+\frac{3040 \left(\frac{5}{4}+\frac{\sqrt{5}}{4}+\frac{\sqrt{14+10 \sqrt{5}}}{4}\right)^{-n}}{11}\right) \left(\left(\sqrt{5}+10\right) \sqrt{14+10 \sqrt{5}}+19 \sqrt{5}+95\right)}{1155200}\)
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This specification was found using the strategy pack "Point Placements" and has 79 rules.

Found on January 18, 2022.

Finding the specification took 1 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_{13}\! \left(x \right) F_{4}\! \left(x \right)\\ F_{4}\! \left(x \right) &= F_{17}\! \left(x \right)+F_{5}\! \left(x \right)\\ F_{5}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{6}\! \left(x \right)\\ F_{6}\! \left(x \right) &= F_{7}\! \left(x \right)\\ F_{7}\! \left(x \right) &= F_{13}\! \left(x \right) F_{8}\! \left(x \right)\\ F_{8}\! \left(x \right) &= F_{5}\! \left(x \right)+F_{9}\! \left(x \right)\\ F_{9}\! \left(x \right) &= F_{10}\! \left(x \right)+F_{14}\! \left(x \right)\\ F_{10}\! \left(x \right) &= F_{11}\! \left(x \right)\\ F_{11}\! \left(x \right) &= F_{12}\! \left(x \right) F_{13}\! \left(x \right)\\ F_{12}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{10}\! \left(x \right)\\ F_{13}\! \left(x \right) &= x\\ F_{14}\! \left(x \right) &= F_{15}\! \left(x \right)\\ F_{15}\! \left(x \right) &= F_{13}\! \left(x \right) F_{16}\! \left(x \right)\\ F_{16}\! \left(x \right) &= F_{14}\! \left(x \right)+F_{6}\! \left(x \right)\\ F_{17}\! \left(x \right) &= F_{18}\! \left(x \right)+F_{24}\! \left(x \right)\\ F_{18}\! \left(x \right) &= F_{19}\! \left(x \right)\\ F_{19}\! \left(x \right) &= F_{13}\! \left(x \right) F_{20}\! \left(x \right)\\ F_{20}\! \left(x \right) &= F_{12}\! \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_{23}\! \left(x \right) &= F_{13}\! \left(x \right) F_{21}\! \left(x \right)\\ F_{24}\! \left(x \right) &= F_{25}\! \left(x \right)+F_{26}\! \left(x \right)+F_{54}\! \left(x \right)\\ F_{25}\! \left(x \right) &= 0\\ F_{26}\! \left(x \right) &= F_{13}\! \left(x \right) F_{27}\! \left(x \right)\\ F_{27}\! \left(x \right) &= F_{28}\! \left(x \right)+F_{39}\! \left(x \right)\\ F_{28}\! \left(x \right) &= F_{29}\! \left(x \right)+F_{6}\! \left(x \right)\\ F_{29}\! \left(x \right) &= F_{15}\! \left(x \right)+F_{25}\! \left(x \right)+F_{30}\! \left(x \right)\\ F_{30}\! \left(x \right) &= F_{13}\! \left(x \right) F_{31}\! \left(x \right)\\ F_{31}\! \left(x \right) &= F_{32}\! \left(x \right)+F_{9}\! \left(x \right)\\ F_{32}\! \left(x \right) &= F_{33}\! \left(x \right)+F_{36}\! \left(x \right)\\ F_{33}\! \left(x \right) &= F_{34}\! \left(x \right)\\ F_{34}\! \left(x \right) &= F_{13}\! \left(x \right) F_{35}\! \left(x \right)\\ F_{35}\! \left(x \right) &= F_{10}\! \left(x \right)+F_{33}\! \left(x \right)\\ F_{36}\! \left(x \right) &= F_{37}\! \left(x \right)\\ F_{37}\! \left(x \right) &= F_{13}\! \left(x \right) F_{38}\! \left(x \right)\\ F_{38}\! \left(x \right) &= F_{14}\! \left(x \right)+F_{36}\! \left(x \right)\\ F_{39}\! \left(x \right) &= F_{24}\! \left(x \right)+F_{40}\! \left(x \right)\\ F_{40}\! \left(x \right) &= 2 F_{25}\! \left(x \right)+F_{41}\! \left(x \right)+F_{44}\! \left(x \right)\\ F_{41}\! \left(x \right) &= F_{13}\! \left(x \right) F_{42}\! \left(x \right)\\ F_{42}\! \left(x \right) &= F_{24}\! \left(x \right)+F_{43}\! \left(x \right)\\ F_{43}\! \left(x \right) &= F_{41}\! \left(x \right)\\ F_{44}\! \left(x \right) &= F_{13}\! \left(x \right) F_{45}\! \left(x \right)\\ F_{45}\! \left(x \right) &= F_{46}\! \left(x \right)+F_{47}\! \left(x \right)\\ F_{46}\! \left(x \right) &= F_{22}\! \left(x \right)+F_{43}\! \left(x \right)\\ F_{47}\! \left(x \right) &= F_{48}\! \left(x \right)+F_{51}\! \left(x \right)\\ F_{48}\! \left(x \right) &= F_{49}\! \left(x \right)\\ F_{49}\! \left(x \right) &= F_{13}\! \left(x \right) F_{50}\! \left(x \right)\\ F_{50}\! \left(x \right) &= F_{22}\! \left(x \right)+F_{48}\! \left(x \right)\\ F_{51}\! \left(x \right) &= F_{52}\! \left(x \right)\\ F_{52}\! \left(x \right) &= F_{13}\! \left(x \right) F_{53}\! \left(x \right)\\ F_{53}\! \left(x \right) &= F_{43}\! \left(x \right)+F_{51}\! \left(x \right)\\ F_{54}\! \left(x \right) &= F_{13}\! \left(x \right) F_{55}\! \left(x \right)\\ F_{55}\! \left(x \right) &= F_{17}\! \left(x \right)+F_{56}\! \left(x \right)\\ F_{56}\! \left(x \right) &= F_{57}\! \left(x \right)+F_{67}\! \left(x \right)\\ F_{57}\! \left(x \right) &= F_{25}\! \left(x \right)+F_{58}\! \left(x \right)+F_{65}\! \left(x \right)\\ F_{58}\! \left(x \right) &= F_{13}\! \left(x \right) F_{59}\! \left(x \right)\\ F_{59}\! \left(x \right) &= F_{60}\! \left(x \right)+F_{61}\! \left(x \right)\\ F_{60}\! \left(x \right) &= F_{10}\! \left(x \right)+F_{33}\! \left(x \right)\\ F_{61}\! \left(x \right) &= F_{22}\! \left(x \right)+F_{62}\! \left(x \right)\\ F_{62}\! \left(x \right) &= F_{63}\! \left(x \right)\\ F_{63}\! \left(x \right) &= F_{13}\! \left(x \right) F_{64}\! \left(x \right)\\ F_{64}\! \left(x \right) &= F_{22}\! \left(x \right)+F_{62}\! \left(x \right)\\ F_{65}\! \left(x \right) &= F_{13}\! \left(x \right) F_{66}\! \left(x \right)\\ F_{66}\! \left(x \right) &= F_{18}\! \left(x \right)+F_{57}\! \left(x \right)\\ F_{67}\! \left(x \right) &= 2 F_{25}\! \left(x \right)+F_{68}\! \left(x \right)+F_{77}\! \left(x \right)\\ F_{68}\! \left(x \right) &= F_{13}\! \left(x \right) F_{69}\! \left(x \right)\\ F_{69}\! \left(x \right) &= F_{70}\! \left(x \right)+F_{72}\! \left(x \right)\\ F_{70}\! \left(x \right) &= F_{14}\! \left(x \right)+F_{71}\! \left(x \right)\\ F_{71}\! \left(x \right) &= F_{37}\! \left(x \right)\\ F_{72}\! \left(x \right) &= F_{43}\! \left(x \right)+F_{73}\! \left(x \right)\\ F_{73}\! \left(x \right) &= F_{74}\! \left(x \right)\\ F_{74}\! \left(x \right) &= F_{13}\! \left(x \right) F_{75}\! \left(x \right)\\ F_{75}\! \left(x \right) &= F_{43}\! \left(x \right)+F_{76}\! \left(x \right)\\ F_{76}\! \left(x \right) &= F_{74}\! \left(x \right)\\ F_{77}\! \left(x \right) &= F_{13}\! \left(x \right) F_{78}\! \left(x \right)\\ F_{78}\! \left(x \right) &= F_{24}\! \left(x \right)+F_{67}\! \left(x \right)\\ \end{align*}\)