OFFSET
0,2
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..40
FORMULA
a(n) = [x^(n^2)] (Sum_{j=-oo..oo} x^(j^2))^(n^2).
a(n) = A066535(n^2).
EXAMPLE
a(2) = 24: 4 = x^2 + y^2 + z^2 + u^2 has 24 solutions (x,y,z,u): 16 permutations of (+/-1,+/-1,+/-1,+/-1) and 8 permutations of (+/-2,0,0,0).
MAPLE
b:= proc(n, t) option remember; `if`(n=0, 1, `if`(n<0 or t<1, 0,
b(n, t-1) +2*add(b(n-j^2, t-1), j=1..isqrt(n))))
end:
a:= n-> b(n^2$2):
seq(a(n), n=0..10);
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Mar 11 2023
STATUS
approved