OFFSET
0,3
FORMULA
a(n) = [x^1] Product_{k=1..n} (x^k + 1 + 1/x^k).
a(n) = [x^(n*(n+1)/2+1)] Product_{k=1..n} (1 + x^k + x^(2*k)).
MATHEMATICA
Table[Coefficient[Product[(x^k + 1 + 1/x^k), {k, 1, n}], x, 1], {n, 0, 31}]
PROG
(Python)
from itertools import count, islice
from collections import Counter
def A369628_gen(): # generator of terms
ccount = Counter({0:1})
yield 0
for i in count(1):
bcount = Counter(ccount)
for a in ccount:
bcount[a+i] += ccount[a]
bcount[a-i] += ccount[a]
ccount = bcount
yield(ccount[1])
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Jan 28 2024
STATUS
approved