OFFSET
0,6
LINKS
Eric Weisstein's World of Mathematics, Polygonal Number
FORMULA
a(n) = [x^p(n,n)] Product_{k=1..n} (1 + x^p(n,k)), where p(n,k) = k * (k * (n - 2) - n + 4) / 2 is the k-th n-gonal number.
EXAMPLE
a(5) = 2 because 5th pentagonal number is 35 and we have [35] and [22, 12, 1].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Sep 19 2020
STATUS
approved