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 A015913 #26 Jul 04 2021 00:14:44 %S A015913 3,7,13,19,37,43,67,79,97,103,109,127,163,193,223,229,277,307,313,349, %T A015913 379,397,439,457,463,487,499,613,643,673,739,757,769,823,853,859,877, %U A015913 883,907,937,967,1009,1087,1093,1213,1279,1297,1303,1423 %N A015913 Numbers k such that sigma(k) + 4 = sigma(k+4). %C A015913 This sequence contains the composite number 305635357, so is different from A023200 and A029710 (305635357 is the only composite member of the present sequence below 10^9). - _Jud McCranie_, Jan 07 2001 %H A015913 Vincenzo Librandi, <a href="/A015913/b015913.txt">Table of n, a(n) for n = 1..1000</a> %t A015913 Select[Range[1500],DivisorSigma[1,#]+4==DivisorSigma[1,#+4]&] (* _Harvey P. Dale_, Nov 04 2011 *) %o A015913 (PARI) is(n)=sigma(n)+4==sigma(n+4) \\ _Charles R Greathouse IV_, Mar 09 2014 %Y A015913 Cf. A023200, A029710. %K A015913 nonn %O A015913 1,1 %A A015913 _Robert G. Wilson v_