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 A274552 #30 Jun 13 2025 10:47:25 %S A274552 2,4,5,6,7,8,15,52,315,592,1155,2102272,815634435 %N A274552 Numbers k such that sigma(k) == 0 (mod k-3). %e A274552 sigma(4) mod (4-3) = 7 mod 1 = 0. %t A274552 k = -3; Select[Range[1, 10^6], # + k != 0 && Mod[DivisorSigma[1, #], # + k] == 0 &] (* _Michael De Vlieger_, Jul 01 2016 *) %o A274552 (Magma) [n: n in [1..2*10^6] | n ne 3 and SumOfDivisors(n) mod (n-3) eq 0 ]; // _Vincenzo Librandi_, Jul 02 2016 %o A274552 (PARI) is(n) = if(n == 3, return(0), Mod(sigma(n), n-3)==0) \\ _Felix Fröhlich_, Jul 02 2016 %Y A274552 Contains subsequence A141548. %Y A274552 Cf. A000203, A067702, A087485, A274551, A274553, A274554, A274556, A274557, A274558, A274559, A274560, A274561, A274562, A274563, A274564, A274565, A274566. %K A274552 nonn,more %O A274552 1,1 %A A274552 _Paolo P. Lava_, Jun 28 2016 %E A274552 a(12)-a(13) from _Giovanni Resta_ %E A274552 a(1)=2 inserted by _Max Alekseyev_, Jun 08 2025