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 A213250 Numbers n such that the coefficient of x^n in the expansion of Product_{k>=1} (1-x^k)^2 is zero. 7

%I

%S 7,11,12,17,18,21,22,25,32,37,39,41,42,43,46,47,49,54,57,58,60,62,65,

%T 67,68,72,74,75,76,81,82,87,88,90,92,95,97,98,99,106,107,109,111,112,

%U 113,116,117,120,122,123,125,126,128,130,132,136,137

%N Numbers n such that the coefficient of x^n in the expansion of Product_{k>=1} (1-x^k)^2 is zero.

%C Indices of zero entries in A002107. Asymptotic density is 1.

%C Contains A093519, numbers with no representation as sum of two or fewer pentagonal numbers.

%H Seiichi Manyama, <a href="/A213250/b213250.txt">Table of n, a(n) for n = 1..10000</a>

%t LongPoly = Series[Product[1 - q^n, {n, 1, 300}]^2, {q, 0, 300}]; ZeroTable = {}; For[i = 1, i < 301, i++, If[Coefficient[LongPoly, q^i] == 0, AppendTo[ZeroTable, i]]]; ZeroTable

%o (PARI)

%o x='x+O('x^200);

%o v=Vec(eta(x)^2 - 1);

%o for(k=1,#v,if(v[k]==0,print1(k,", ")));

%o /* _Joerg Arndt_, Jun 07 2012 */

%Y Cf. A093519.

%Y Numbers k such that the coefficient of x^k in the expansion of Product_{j>=1} (1 - x^j)^m is zero: A090864 (m=1), this sequence (m=2), A014132 (m=3), A302056 (m=4), A302057 (m=5), A020757 (m=6), A322043 (m=15).

%K easy,nonn

%O 1,1

%A _William J. Keith_, Jun 07 2012

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Last modified February 23 16:10 EST 2020. Contains 332171 sequences. (Running on oeis4.)