OFFSET
0,3
FORMULA
a(n)=sum(k=1..n, binomial(2*n,k)*(sum(i=0..k/2, (2*i-k)^(2*n-k)*binomial(k,i)*(-1)^(n-i)))/(2^k))/n, n>0, a(0)=1.
PROG
(Maxima)
a(n):=sum(binomial(2*n, k)*(sum((2*i-k)^(2*n-k)*binomial(k, i)*(-1)^(n-i), i, 0, k/2))/(2^k), k, 1, n)/n;
CROSSREFS
KEYWORD
sign
AUTHOR
Vladimir Kruchinin, May 30 2011
STATUS
approved