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 A303480 #14 Apr 26 2018 07:47:36 %S A303480 1,3,4,17,53,433,456,901,1052,4011,14504,15111,156408,245423,328408, %T A303480 911340,2263141,13736475,20092485,37903271,60003559,78733423,84206981, %U A303480 234095587,319691535,986119609,1488787296,6139123252,8663152552,11909530004,19226378456,65827587400 %N A303480 Numbers k such that the average of squarefree kernels of all positive integers <= k is an integer. %C A303480 Numbers k such that k | A073355(k). %H A303480 Wikipedia, <a href="https://en.wikipedia.org/wiki/Radical_of_an_integer">Radical of an integer</a> %e A303480 3 is a term because the first 3 terms of A007947 are 1, 2 and 3 whose sum is divisible by 3. %o A303480 (PARI) isok(k) = sum(i=1, k, factorback(factor(i)[, 1])) % k == 0; \\ _Michel Marcus_, Apr 25 2018 %Y A303480 Cf. A007947, A073355, A226647, A284755, A285510. %K A303480 nonn %O A303480 1,2 %A A303480 _Ilya Gutkovskiy_, Apr 24 2018 %E A303480 a(13)-a(17) from _Alois P. Heinz_, Apr 24 2018 %E A303480 a(18)-a(26) from _Daniel Suteu_, Apr 24 2018 %E A303480 a(27)-a(32) from _Giovanni Resta_, Apr 26 2018