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 A097015 #13 Dec 12 2024 11:09:24 %S A097015 1,1,2401,2614689,36324729,36324729,2411675443849,2411675443849, %T A097015 12361036649679601 %N A097015 Smallest k such that sigma(k) + 1 is divisible by primorial(n). %C A097015 10^19 < a(9) <= 725298909352131113041. Terms a(3) through a(8) all have the prime signature p^4*q^2*r^2. Any x such that sigma(x) = -1 (mod 30) must have at least eight prime factors. However, for all n, there are solutions with fewer than three distinct prime factors. More generally, for any k > 1, let p be a prime of the form mk+1; then sigma(p^(k-2)) = -1 (mod k). For a(9), 725298909352131113041 is the least solution with eight prime factors. I have not been able to rule out a smaller solution with more prime factors. - _David Wasserman_, Dec 14 2007 %F A097015 a(n) = A233929(A002110(n)). - _Andrew Howroyd_, Dec 12 2024 %Y A097015 Cf. A002110 (primorial), A084301, A084303, A000203, A097011, A097012, A097014, A233929. %K A097015 nonn %O A097015 0,3 %A A097015 _Labos Elemer_, Aug 19 2004 %E A097015 More terms from _David Wasserman_, Dec 14 2007 %E A097015 a(0)=1 prepended by _Andrew Howroyd_, Dec 12 2024