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 A260420 #17 Sep 08 2022 08:46:13 %S A260420 2,3,23,14927,31049,69107,246263,5860169,307164671,881198663, %T A260420 1489455647,2386555631,8225563703,14311679063,111494234183, %U A260420 154357775303,299004519623,870455062823,970388922263,991817878343,1677028870823,1782783762503,1830446935223 %N A260420 Numbers n such that sigma(n+1) - sigma(n-1) = n+1. %C A260420 Proposed by _Jaroslav Krizek_ in A260071. %C A260420 Also: numbers n such that A001065(n+1) = A000203(n-1). %H A260420 Giovanni Resta, <a href="/A260420/b260420.txt">Table of n, a(n) for n = 1..33</a> (terms < 10^13) %F A260420 a(n) = A246852(n) + 1. %t A260420 Select[Range@ 1000000, DivisorSigma[1, # + 1] - DivisorSigma[1, # - 1] == # + 1 &] (* _Michael De Vlieger_, Jul 25 2015 *) %o A260420 (PARI) for(n=2,1e9,sigma(n+1)-sigma(n-1)==n+1&&print1(n",")) %o A260420 (Magma) [n: n in [2..5*10^6] | DivisorSigma(1, n+1) - DivisorSigma(1, n-1) eq n+1]; // _Vincenzo Librandi_, Jul 26 2015 %Y A260420 Cf. A260071, A076530, A246852. %K A260420 nonn %O A260420 1,1 %A A260420 _M. F. Hasler_, Jul 25 2015