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 A072864 #12 Jul 31 2025 14:31:02 %S A072864 7,13,14,19,21,26,28,31,35,37,38,39,42,43,52,56,57,61,62,63,65,67,70, %T A072864 73,74,76,77,78,79,84,86,91,93,95,97,103,104,105,109,111,112,114,117, %U A072864 119,122,124,126,127,129,130,133,134,139,140,143,146,148,151,152,154 %N A072864 Numbers m such that the smallest k dividing sigma(k*m^2) is equal to 3. %C A072864 Sequence contains primes of the form 6x+1 (A002476) and multiples of those primes, except (6x+1)^2. If x is not in the sequence, the smallest k dividing sigma(k*x^2) is equal to 6. %o A072864 (PARI) isok(n) = A049605(n^2) != 6; \\ _Michel Marcus_, Nov 21 2013 %Y A072864 Cf. A049605. %K A072864 easy,nonn %O A072864 1,1 %A A072864 _Benoit Cloitre_, Jul 27 2002