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A086781 a(n) is the number of nonzero terms in the expansion of (x-y) * (x^2-y^2) * (x^3-y^3) * ... * (x^n-y^n). 7
1, 2, 4, 6, 7, 12, 14, 18, 25, 32, 36, 42, 53, 68, 64, 84, 97, 108, 126, 146, 161, 170, 192, 208, 229, 246, 274, 300, 333, 348, 372, 400, 427, 468, 492, 526, 561, 602, 626, 644, 691, 736, 772, 826, 869, 902, 930, 974, 1017, 1062, 1120, 1184, 1223, 1262, 1314, 1374, 1419, 1468, 1518, 1586, 1663, 1718, 1778, 1834, 1899, 1954, 2018 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

COMMENTS

In the definition one can take y=1. - Emeric Deutsch, Jan 01 2008

LINKS

Joerg Arndt, Table of n, a(n) for n = 0..1000

MAPLE

a:=proc(n) options operator, arrow: nops(expand(product(x^j-y^j, j=1..n))) end proc: seq(a(n), n=0..50); # Emeric Deutsch, Jan 01 2008

MATHEMATICA

Table[Length[Expand[Times@@(x^Range[n]-1)]], {n, 50}] (* Harvey P. Dale, Mar 01 2012 *)

PROG

(PARI) a(n)=#select(w->w, Vec(prod(k=1, n, 1-'x^k))); \\ Joerg Arndt, Apr 12 2017

CROSSREFS

Cf. A000124, A086376.

Sequence in context: A051730 A070317 A138398 * A261220 A272589 A191191

Adjacent sequences:  A086778 A086779 A086780 * A086782 A086783 A086784

KEYWORD

nonn

AUTHOR

Yuval Dekel (dekelyuval(AT)hotmail.com), Aug 03 2003

EXTENSIONS

More terms from Emeric Deutsch, Jan 01 2008

a(0)=1 prepended by Alois P. Heinz, Apr 12 2017

STATUS

approved

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Last modified September 20 20:51 EDT 2018. Contains 315243 sequences. (Running on oeis4.)