OFFSET
0,2
COMMENTS
a(n) >= A160089(n) with equality only for n=0. - Michel Marcus, Jun 12 2013
LINKS
Seiichi Manyama, Table of n, a(n) for n = 0..1000
FORMULA
a(n) := |c(n, 0)| + |c(n, 1)| + ... + |c(n, n(n+1)/2)| where c(n, j) are the coefficients of the polynomial P(n, x) := (1-x)(1-x^2)(1-x^3)...(1-x^n)
EXAMPLE
a(1) = 1+1 = 2; a(4) = Length(P(4,x)) = Length(1 - x - x^2 + 2x^5 - x^8 - x^9 + x^10) = 1+1+1+2+1+1+1 = 8
PROG
(PARI) a(n) = {pol = prod(i=1, n, 1-x^i); return (sum(i=0, poldegree(pol), abs(polcoeff(pol, i)))); } \\ Michel Marcus, Jun 12 2013
CROSSREFS
KEYWORD
nonn
AUTHOR
Steffen Eckmann (steffen.eckmann(AT)eon.com), May 17 2001
EXTENSIONS
a(0)=1 prepended by Seiichi Manyama, May 03 2018
STATUS
approved