A365268 G.f. satisfies A(x) = 1 + x*A(x)^2*(1 + x^3*A(x)^2).
1, 1, 2, 5, 15, 48, 160, 549, 1929, 6909, 25134, 92612, 344924, 1296376, 4910656, 18728645, 71857133, 277160183, 1074085446, 4180057725, 16329796959, 64014638564, 251734985808, 992788252700, 3925688845948, 15560762343388, 61818928594952
Offset: 0
Keywords
Programs
-
PARI
a(n) = sum(k=0, n\4, binomial(n-3*k, k)*binomial(2*n-4*k+1, n-3*k)/(2*n-4*k+1));
Formula
a(n) = Sum_{k=0..floor(n/4)} binomial(n-3*k,k) * binomial(2*n-4*k+1,n-3*k)/(2*n-4*k+1).