OFFSET
0,7
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..2926
A. Goupil, M.-E. Pellerin and J. de Wouters d'oplinter, Snake Polyominoes, arXiv preprint arXiv:1307.8432 [math.CO], 2013-2014. (Gives a g.f.)
FORMULA
G.f. A(x) satisfies: A(x) = (1 + x^2 * A(x)^2) / (1 - x + x^2 + x^3 + x^4 + x^5). - Ilya Gutkovskiy, Jul 20 2021
MATHEMATICA
a[0]=1; a[n_]:= a[n]=a[n-1] + Sum[a[k]*a[n-2-k], {k, 4, n-2}]; Table[a[n], {n, 0, 30}] (* modified by G. C. Greubel, Jan 01 2018 *)
B[q_] = (q^2 + q^3 + q^4 + q^5 - Sqrt[((q(q^5 - 1))/(q - 1) - 1)^2 - 4q^6] - q + 1)/(2q^2); CoefficientList[B[q] + O[q]^31, q] (* Jean-François Alcover, Jan 29 2019 *)
PROG
(PARI) {a(n) = if(n==0, 1, a(n-1) + sum(k=4, n-2, a(k)*a(n-k-2)))};
for(n=0, 30, print1(a(n), ", ")) \\ G. C. Greubel, Jan 01 2018
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved