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 A072188 #18 Aug 20 2021 22:49:25 %S A072188 2,5,7,33,18336,19262,38184,54722,458010,1402224,1473624,1708480, %T A072188 3680560,3733584,5829841,7769904,13204262,72873362,136910448, %U A072188 252961224,509874800,1138081558,3414097921,5440847376,7285326504,8986032648,14409659936,15953956256,23556877704 %N A072188 Numbers k that divide sigma(k-1)+sigma(k)+sigma(k+1), where sigma() is the "sum of integer divisors" function. %C A072188 Heuristics would seem to indicate that this sequence is infinite and sparse. Compare this sequence to the positive integers k that divide sigma(k) - the perfect and multiperfect numbers. %H A072188 Giovanni Resta, <a href="/A072188/b072188.txt">Table of n, a(n) for n = 1..36</a> (terms < 10^13) %e A072188 33 is in this list because sigma(32) + sigma(33) + sigma(34) = 63 + 48 + 54 = 165 = 33*5. %o A072188 (PARI) for(i=2,99999,if((sigma(i-1)+sigma(i)+sigma(i+1))%i==0,print(i))) %Y A072188 Cf. A007691. %K A072188 nonn %O A072188 1,1 %A A072188 _Jack Brennen_, Jul 01 2002 %E A072188 More terms from _Jason Earls_, Aug 25 2002 %E A072188 a(18)-a(26) from _Donovan Johnson_, Feb 01 2009 %E A072188 a(27)-a(29) from _Donovan Johnson_, Sep 17 2013