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 A247205 #60 Jun 27 2024 22:21:41 %S A247205 1,18480,8388480 %N A247205 Numbers k such that 2*k^2 - 1 divides 2^k - 1. %C A247205 a(4) > 2*10^10. - _Chai Wah Wu_, Dec 06 2014 %e A247205 1 is in this sequence because 2*1^2 - 1 = 1 divides 2^1 - 1 = 1. %o A247205 (Magma) [n: n in [1..100000] | Denominator((2^n-1)/(2*n^2-1)) eq 1]; %o A247205 (PARI) for(n=1,10^9,if(Mod(2,2*n^2-1)^n==+1,print1(n,", "))); \\ _Joerg Arndt_, Nov 30 2014 %Y A247205 Cf. A247219, A247221. %K A247205 nonn,more,bref %O A247205 1,2 %A A247205 _Juri-Stepan Gerasimov_, Nov 30 2014 %E A247205 a(3) from _Joerg Arndt_, Nov 30 2014