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 A259174 #23 Aug 28 2025 15:52:53 %S A259174 12,20,56,70,88,104,108,220,368,464,550,572,650,748,836,860,952,992, %T A259174 1232,1504,1672,1888,1952,2140,2392,2744,3708,4030,5336,5830,6328, %U A259174 6536,6808,7192,7304,7544,7912,8968,9656,9820,10184,10792,11096,13496,14008 %N A259174 Numbers whose abundance is a power of 2. %C A259174 Subsequence of A005101 whose abundance is a term of A000079 except 1. %C A259174 Below 35*10^8, only 236925 is odd and its abundance is 2^9. %C A259174 Least terms with abundance 2^e for e = 1, 2, ... are listed in A292558. %H A259174 Robert G. Wilson v, <a href="/A259174/b259174.txt">Table of n, a(n) for n = 1..482</a> %t A259174 fQ[n_] := IntegerQ@ Log2[DivisorSigma[1, n] - 2 n]; Select[ Range@ 15000, fQ] %o A259174 (PARI) isok(n) = isprimepower(sigma(n)-2*n, &p) && (p==2); \\ _Michel Marcus_, Mar 25 2017 %Y A259174 Contains as subsequences A088831, A088832, A088833, A141547, A175989, A275996, A292626. %Y A259174 Cf. A005101, A292558. %K A259174 nonn,changed %O A259174 1,1 %A A259174 _Robert G. Wilson v_, Jun 20 2015