cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A278779 Numbers m such that A000041(m) is of the form 2^2 * k for odd k.

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%I A278779 #17 May 25 2024 09:08:23
%S A278779 26,30,55,58,59,62,74,78,80,84,100,108,112,113,117,124,126,135,153,
%T A278779 187,191,200,205,258,265,280,291,310,317,323,336,337,342,344,351,352,
%U A278779 353,358,359,365,374,380,384,404,409,416,444,445,458,481,485,492,501,503
%N A278779 Numbers m such that A000041(m) is of the form 2^2 * k for odd k.
%C A278779 Numbers m such that A278478(m) = 2.
%C A278779 Also numbers m such that A000041(m) has twice as many even divisors as odd divisors.
%H A278779 Colin Barker, <a href="/A278779/b278779.txt">Table of n, a(n) for n = 1..1000</a>
%F A278779 A000041(a(n)) = A278196(n).
%t A278779 Select[Range[3000], IntegerExponent[PartitionsP[#], 2] == 2 &] (* _Amiram Eldar_, May 25 2024 *)
%o A278779 (PARI) isok(n) = valuation(numbpart(n), 2)==2;
%o A278779 select(n->isok(n), vector(1000, n, n))
%Y A278779 Cf. A000041, A278196, A278780, A278781, A278782, A278783, A278784.
%Y A278779 Positions of 2's in A278478.
%K A278779 nonn
%O A278779 1,1
%A A278779 _Colin Barker_, Nov 28 2016