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.
%I A252891 #25 Jul 18 2025 05:19:34 %S A252891 1,2,4,8,20,26,28,29,39,41,129,430,526,591,655,731,1388,1622,2249, %T A252891 3734,6841,18752,18772,21332,35017,37337,53173,105557,113377,124753, %U A252891 419029,614153,824149,829333,2192923,2369654,2538915,3059853,3388115,3479244,3557183 %N A252891 Numbers m such that sigma(m) is a partition number. %H A252891 Robert G. Wilson v, <a href="/A252891/b252891.txt">Table of n, a(n) for n = 1..65</a> %e A252891 26 is in the sequence because the sum of divisors of 26 is 1 + 2 + 13 + 26 = 42 and 42 is a partition number because the number of partitions of 10 is equal to 42. %t A252891 (* To extend the search beyond 50400, be sure to increase the length of partNums accordingly *) partNums = PartitionsP[Range[50]]; Select[Range[100], MemberQ[partNums, DivisorSigma[1, #]] &] (* _Alonso del Arte_, Dec 24 2014 *) %Y A252891 Cf. A000041, A000203. %K A252891 nonn %O A252891 1,2 %A A252891 _Omar E. Pol_, Dec 24 2014 %E A252891 a(11)-a(16) from _Alonso del Arte_, Dec 24 2014 %E A252891 More terms from _Michel Marcus_, Dec 27 2014