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 A054027 #16 Jun 13 2025 11:58:35 %S A054027 2,3,4,5,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27, %T A054027 29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51, %U A054027 52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74 %N A054027 Numbers that do not divide their sum of divisors. %C A054027 Does not contain numbers like 1, 120, 672, 30240, 32760, 523776,.. which are in A132999. - _R. J. Mathar_, Jun 13 2025 %p A054027 with(numtheory): [seq(`if`(sigma(i) mod i <> 0,i,print( )),i=1..90)]; %t A054027 Select[Range[100],!Divisible[DivisorSigma[1,#],#]&] (* _Harvey P. Dale_, May 29 2019 *) %o A054027 (PARI) isok(m) = (sigma(m) % m) != 0; \\ _Michel Marcus_, Jun 20 2021 %Y A054027 Complement of A007691. Cf. A000203, A054024. %K A054027 nonn %O A054027 1,1 %A A054027 _Asher Auel_, Jan 19 2000