###### Av(123, 132, 3241)
Generating Function
$$\displaystyle \frac{x^{3}-x +1}{\left(x -1\right) \left(x^{2}+x -1\right)}$$
Counting Sequence
1, 1, 2, 4, 7, 12, 20, 33, 54, 88, 143, 232, 376, 609, 986, ...
Implicit Equation for the Generating Function
$$\displaystyle \left(x -1\right) \left(x^{2}+x -1\right) F \! \left(x \right)-x^{3}+x -1 = 0$$
Recurrence
$$\displaystyle a \! \left(0\right) = 1$$
$$\displaystyle a \! \left(1\right) = 1$$
$$\displaystyle a \! \left(2\right) = 2$$
$$\displaystyle a \! \left(3\right) = 4$$
$$\displaystyle a \! \left(n +2\right) = a \! \left(n \right)+a \! \left(n +1\right)+1, \quad n \geq 4$$
Explicit Closed Form
$$\displaystyle \left\{\begin{array}{cc}1 & n =0 \\ \frac{\left(-3 \sqrt{5}+5\right) \left(-\frac{\sqrt{5}}{2}-\frac{1}{2}\right)^{-n}}{10}-1+\frac{\left(3 \sqrt{5}+5\right) \left(\frac{\sqrt{5}}{2}-\frac{1}{2}\right)^{-n}}{10} & \text{otherwise} \end{array}\right.$$

### This specification was found using the strategy pack "Point Placements" and has 15 rules.

Found on January 17, 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_{4}\! \left(x \right) F_{5}\! \left(x \right)\\ F_{4}\! \left(x \right) &= x\\ F_{5}\! \left(x \right) &= F_{6}\! \left(x \right)+F_{7}\! \left(x \right)\\ F_{6}\! \left(x \right) &= F_{1}\! \left(x \right)+F_{4}\! \left(x \right)\\ F_{7}\! \left(x \right) &= F_{2}\! \left(x \right)+F_{8}\! \left(x \right)\\ F_{8}\! \left(x \right) &= F_{10}\! \left(x \right)+F_{14}\! \left(x \right)+F_{9}\! \left(x \right)\\ F_{9}\! \left(x \right) &= 0\\ F_{10}\! \left(x \right) &= F_{11}\! \left(x \right) F_{4}\! \left(x \right)\\ F_{11}\! \left(x \right) &= F_{12}\! \left(x \right)+F_{13}\! \left(x \right)\\ F_{12}\! \left(x \right) &= F_{4}\! \left(x \right)\\ F_{13}\! \left(x \right) &= F_{10}\! \left(x \right)\\ F_{14}\! \left(x \right) &= F_{2}\! \left(x \right) F_{4}\! \left(x \right)\\ \end{align*}