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A110525
Expansion of 1/(1-x^2*c(3x)), c(x) the g.f. A000108.
2
1, 0, 1, 3, 19, 141, 1180, 10593, 99712, 971067, 9702388, 98899638, 1024429861, 10752006033, 114097140757, 1222113460332, 13195550763793, 143470913825427, 1569448022488435, 17261100136608984, 190752895126918819
OFFSET
0,4
COMMENTS
Diagonal sums of A110518.
LINKS
FORMULA
a(n) = Sum_{k=0..floor(n/2)} (k/(n-k))*C(2*n-3*k-1, n-2*k)*3^(n-2*k).
MATHEMATICA
Join[{1}, Table[Sum[(k/(n - k))*Binomial[2*n - 3*k - 1, n - 2*k]*3^(n - 2*k), {k, 0, Floor[n/2]}], {n, 1, 50}]] (* G. C. Greubel, Aug 30 2017 *)
PROG
(PARI) concat([1], for(n=1, 25, print1(sum(k=0, n\2, (k/(n - k))*binomial(2*n - 3*k - 1, n - 2*k)*3^(n - 2*k)), ", "))) \\ G. C. Greubel, Aug 30 2017
CROSSREFS
Sequence in context: A025571 A221266 A082758 * A331716 A058859 A291964
KEYWORD
easy,nonn
AUTHOR
Paul Barry, Jul 24 2005
STATUS
approved