OFFSET
0,4
FORMULA
a(n)=sum(k=1..n, (((-1)^(n-3*k)+1)*sum(i=0..(3*k)/2, (2*i-3*k)^n*binomial(3*k,i)*(-1)^((n+3*k)/2-i)))/2^(3*k)), n>0, a(0)=1.
MATHEMATICA
With[{nn=30}, CoefficientList[Series[1/(1-Sin[x]^3), {x, 0, nn}], x] Range[ 0, nn]!] (* Harvey P. Dale, Oct 11 2011 *)
PROG
(Maxima)
a(n):=sum((((-1)^(n-3*k)+1)*sum((2*i-3*k)^n*binomial(3*k, i)*(-1)^((n+3*k)/2-i), i, 0, (3*k)/2))/2^(3*k), k, 1, n);
CROSSREFS
KEYWORD
sign
AUTHOR
Vladimir Kruchinin, Jun 11 2011
STATUS
approved