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 A275370 #15 Jul 14 2017 04:15:21 %S A275370 1,13545,57645,116865,1440495,7029855,8596455,27361125,41100345, %T A275370 48289185,56122185,77560065,103225185,134813385,146591235,163817745, %U A275370 188358885,198748305,242668335,269436375,352094715,358841385,535135965,563911335,636719265,712457655,724692045 %N A275370 Odd numbers n such that sigma(n) = sigma(2*n-1). %C A275370 The smallest term that is not divisible by 5 is 1577106531. %H A275370 Giovanni Resta, <a href="/A275370/b275370.txt">Table of n, a(n) for n = 1..164</a> (terms < 2*10^11) %e A275370 The numbers n that solve sigma(n) = sigma(2n-1) are n = 1, 6, 348, 496, 1420, 1854, 4647, 5352, 6424, 13545, 21126,... The sequence selects the odd members. %o A275370 (PARI) isok(n) = sigma(n) == sigma(2*n-1) && n % 2 == 1 %Y A275370 Cf. A000203, A008438, A272553. %K A275370 nonn %O A275370 1,2 %A A275370 _Altug Alkan_, Jul 25 2016