OFFSET
1,2
LINKS
Andrew Howroyd, Table of n, a(n) for n = 1..1000
FORMULA
G.f.: Sum_{k>=1} x^k*(1 - x^k)/((1 - x)*(1 - 2*x + x^2 - x^k)). - Andrew Howroyd, Apr 13 2021
EXAMPLE
a(4) = 31 = (1 + 3 + 6 + 21) since row 4 of triangle A171843 = (1, 3, 6, 21).
PROG
(PARI) seq(n)={Vec(sum(k=1, n, x^k*(1 - x^k)/((1 - x)*(1 - 2*x + x^2 - x^k)) + O(x*x^n)))} \\ Andrew Howroyd, Apr 13 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Gary W. Adamson, Dec 19 2009
EXTENSIONS
a(10) and a(13) corrected and a(14) and beyond from Andrew Howroyd, Apr 13 2021
STATUS
approved