OFFSET
0,4
FORMULA
a(0) = a(1) = 1; a(n+2) = -Sum_{k=0..n} a(k)*a(n-k).
EXAMPLE
G.f.: A(x) = 1 + x - x^2 - 2*x^3 + x^4 + 6*x^5 + x^6 - 18*x^7 - 16*x^8 + 50*x^9 + 93*x^10 - 112*x^11 - 428*x^12 + ...
MATHEMATICA
terms = 35; A[_] = 0; Do[A[x_] = 1 + x - x^2 A[x]^2 + O[x]^(terms + 1) // Normal, {terms + 1}]; CoefficientList[A[x], x]
a[0] = a[1] = 1; a[n_] := a[n] = -Sum[a[k] a[n - k - 2], {k, 0, n - 2}]; Table[a[n], {n, 0, 35}]
CROSSREFS
KEYWORD
sign
AUTHOR
Ilya Gutkovskiy, Apr 06 2019
STATUS
approved