OFFSET
0,2
LINKS
Harvey P. Dale, Table of n, a(n) for n = 0..1000
Index entries for linear recurrences with constant coefficients, signature (-1, 2, 4, 2).
FORMULA
a(n) = (n+1)*Sum_{k=0..n}(Sum_{l=0..n-k}(binomial(k+1,l)*2^l*(-1)^(n-l-k)*binomial(n-2*l,n-l-k))/(k+1)).
MATHEMATICA
LinearRecurrence[{-1, 2, 4, 2}, {1, 3, 7, 7}, 50] (* Harvey P. Dale, Apr 11 2017 *)
PROG
(Maxima)
a(n):=(n+1)*sum(sum(binomial(k+1, l)*2^l*(-1)^(n-l-k)*binomial(n-2*l, n-l-k), l, 0, n-k)/(k+1), k, 0, n);
CROSSREFS
KEYWORD
nonn
AUTHOR
Vladimir Kruchinin, Mar 15 2016
STATUS
approved