OFFSET
0,3
COMMENTS
Diagonal sums of number triangle A124279.
LINKS
Index entries for linear recurrences with constant coefficients, signature (1,1,-1,1).
FORMULA
a(n) = sum{k=0..floor(n/2), sum{j=0..n-2k, C(j,n-2k-j)C(k,n-2k-j)}}.
a(n) = a(n-1)+a(n-2)-a(n-3)+a(n-4), a(0)=1, a(1)=1, a(2)=2, a(3)=2. - Carl Najafi, May 06 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Oct 24 2006
STATUS
approved