OFFSET
0,2
COMMENTS
FORMULA
G.f.: A(x) = Product_{n>=1} ( 1 - (n+1)*x^n + n*x^(n+1) ) . G.f.: A(x) = Product_{n>=1} [ (1-x)*(1 + x + x^2 +...+ x^(n-1) - n*x^n) ] .
EXAMPLE
A(x) = (1 - 2x + x^2)(1 - 3x^2 + 2x^3)(1 - 4x^3 + 3x^4)(1 - 5x^4 + 4x^5)*...
Terms are even except at positions given by:
a(n) == 1 (mod 2) at n = [0, 4, 8, 20, 28, 48, 60, 88,...,4*A001318(n),...].
PROG
(PARI) a(n)=if(n==0, 1, polcoeff(prod(k=1, n, 1-(k+1)*x^k+k*x^(k+1)+x*O(x^n)), n))
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Apr 10 2007
STATUS
approved