A231621 a(n) = A000930(n*(n+1)/2), where A000930 is Narayana's cows sequence.

1, 1, 2, 6, 28, 189, 1873, 27201, 578949, 18059374, 825604416, 55315679788, 5431645680297, 781666575692345, 164861247948842305, 50959194632488457965, 23085190353310504913320, 15326793132326730009566200, 14913379277290330452859885202, 21267074956884103635776195255433, 44447403127130268192387935737712641

Offset: 0

Author

Paul D. Hanna, Nov 13 2013

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 0..100

Crossrefs

Cf. A000930, A231620.

Programs

Mathematica

Table[SeriesCoefficient[1/(1 - x - x^3), {x, 0, n*(n + 1)/2}], {n,0,50}] (* G. C. Greubel, Apr 26 2017 *)

PARI

{a(n) = polcoeff(1/(1-x-x^3 + x*O(x^(n*(n+1)/2))), n*(n+1)/2)}
for(n=0, 20, print1(a(n), ", "))

Formula

a(n) = [x^(n*(n+1)/2)] 1 / (1 - x - x^3) for n>=0.