Av(1243, 1342, 2143, 2413, 2431, 3142, 4132)
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Generating Function
\(\displaystyle \frac{\left(-2 x^{2}+3 x -1\right) \sqrt{1-4 x}+2 x^{4}+2 x^{2}-3 x +1}{4 x^{3}-6 x^{2}+2 x}\)
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Counting Sequence
1, 1, 2, 6, 17, 49, 147, 460, 1493, 4989, 17051, 59297, 209035, 744947, 2678535, ...
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Implicit Equation for the Generating Function
\(\displaystyle x \left(2 x -1\right)^{2} \left(x -1\right)^{2} F \left(x \right)^{2}-\left(2 x -1\right) \left(x -1\right) \left(2 x^{4}+2 x^{2}-3 x +1\right) F \! \left(x \right)+x^{7}+2 x^{5}+x^{4}-11 x^{3}+13 x^{2}-6 x +1 = 0\)
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Recurrence
\(\displaystyle a \! \left(0\right) = 1\)
\(\displaystyle a \! \left(1\right) = 1\)
\(\displaystyle a \! \left(2\right) = 2\)
\(\displaystyle a \! \left(3\right) = 6\)
\(\displaystyle a \! \left(4\right) = 17\)
\(\displaystyle a \! \left(5\right) = 49\)
\(\displaystyle a \! \left(6\right) = 147\)
\(\displaystyle a \! \left(n +3\right) = \frac{8 \left(1+2 n \right) a \! \left(n \right)}{n +4}-\frac{4 \left(8+5 n \right) a \! \left(n +1\right)}{n +4}+\frac{2 \left(11+4 n \right) a \! \left(n +2\right)}{n +4}+\frac{3 n -6}{n +4}, \quad n \geq 7\)
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This specification was found using the strategy pack "Point Placements" and has 19 rules.

Found on July 23, 2021.

Finding the specification took 1 seconds.

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\(\begin{align*} F_{0}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{2}\! \left(x \right)\\ F_{1}\! \left(x \right) &= 1\\ F_{2}\! \left(x \right) &= F_{3}\! \left(x \right)\\ F_{3}\! \left(x \right) &= F_{12}\! \left(x \right) F_{4}\! \left(x \right)\\ F_{4}\! \left(x \right) &= F_{0}\! \left(x \right)+F_{5}\! \left(x \right)\\ F_{5}\! \left(x \right) &= F_{6}\! \left(x \right)\\ F_{6}\! \left(x \right) &= F_{12}\! \left(x \right) F_{7}\! \left(x \right)\\ F_{7}\! \left(x \right) &= F_{13}\! \left(x \right)+F_{8}\! \left(x \right)\\ F_{8}\! \left(x \right) &= F_{9} \left(x \right)^{3}\\ F_{9}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{10}\! \left(x \right)\\ F_{10}\! \left(x \right) &= F_{11}\! \left(x \right)\\ F_{11}\! \left(x \right) &= F_{9} \left(x \right)^{2} F_{12}\! \left(x \right)\\ F_{12}\! \left(x \right) &= x\\ F_{13}\! \left(x \right) &= F_{12}\! \left(x \right) F_{14}\! \left(x \right) F_{16}\! \left(x \right)\\ F_{14}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{15}\! \left(x \right)\\ F_{15}\! \left(x \right) &= F_{12}\! \left(x \right) F_{14}\! \left(x \right)\\ F_{16}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{17}\! \left(x \right)\\ F_{17}\! \left(x \right) &= F_{18}\! \left(x \right)\\ F_{18}\! \left(x \right) &= F_{12}\! \left(x \right) F_{14}\! \left(x \right) F_{16}\! \left(x \right)\\ \end{align*}\)