OFFSET
0,6
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..7939
Eric Weisstein's World of Mathematics, Square Pyramidal Number
FORMULA
G.f.: 1/(1 - Sum_{k>=1} x^(k*(k+1)*(2*k+1)/6)).
MAPLE
h:= proc(n) option remember; `if`(n<1, 0, (t->
`if`(t*(t+1)*(2*t+1)/6>n, t-1, t))(1+h(n-1)))
end:
a:= proc(n) option remember; `if`(n=0, 1,
add(a(n-i*(i+1)*(2*i+1)/6), i=1..h(n)))
end:
seq(a(n), n=0..60); # Alois P. Heinz, Dec 28 2018
MATHEMATICA
nmax = 49; CoefficientList[Series[1/(1 - Sum[x^(k (k + 1) (2 k + 1)/6), {k, 1, nmax}]), {x, 0, nmax}], x]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 26 2018
STATUS
approved