OFFSET
0,2
COMMENTS
Diagonal sums of number triangle A115284.
LINKS
Index entries for linear recurrences with constant coefficients, signature (2,-1,1,-2,1).
FORMULA
G.f.: (1+x)^2*(1+x^2)^2/((1-x)(1-x^2)(1-x^3)); a(n)=sum{k=0..floor(n/2), sum{j=0..n-k [j<=k]*(4-C(1, k-j)-2C(0, k-j))*[j<=n-2k]*((4-C(1, n-2k-j)-2C(0, n-2k-j))}}.
MATHEMATICA
LinearRecurrence[{2, -1, 1, -2, 1}, {1, 3, 7, 14, 23, 35}, 50] (* Harvey P. Dale, Jul 27 2015 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jan 19 2006
STATUS
approved