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 A073500 #34 May 09 2025 07:13:56
%S A073500 954,1300,11142,38214,89484,152154,167784,254136,303280,473316,574716,
%T A073500 813920,918080,1307022,2008360,3676242,9878244,10368512,12548754,
%U A073500 19411480,22493262,42413484,77766486,81513816,157874000,240828972
%N A073500 Numbers k such that sigma(k) = sigma(k+1)+sigma(k-1).
%H A073500 Giovanni Resta, <a href="/A073500/b073500.txt">Table of n, a(n) for n = 1..170</a> (terms < 10^13, first 50 terms from Donovan Johnson)
%F A073500 a(n) = A076528(n)-1 - _Alex Ratushnyak_, Jul 06 2013.
%t A073500 s1 = s2 = s3 = 0; Do[ s1 = s2; s2 = s3; s3 = DivisorSigma[1, n]; If[ s2 == s1 + s3, Print[n - 1]], {n, 1, 10^8}]
%o A073500 (PARI) list(lim) = {my(s1 = 0, s2 = 0, s3); for(k = 1, lim, s3 = sigma(k); if(s2 == s1 + s3, print1(k-1, ", ")); s1 = s2; s2 = s3);} \\ _Amiram Eldar_, May 09 2025
%Y A073500 Cf. A000203 (sigma), A076528.
%K A073500 nonn
%O A073500 1,1
%A A073500 _Benoit Cloitre_, Aug 27 2002
%E A073500 Edited and extended by _Robert G. Wilson v_, Oct 24 2002
%E A073500 a(25)-a(26) from _Donovan Johnson_, Feb 01 2009