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 A242270 #16 Sep 08 2022 08:46:08 %S A242270 6,8,10,14,15,60,90,114,118,204,350,390 %N A242270 Numbers k such that k*7^k+1 is semiprime. %C A242270 The semiprimes of this form are: 705895, 46118409, 2824752491, 9495123019887, 71213422649146, ... %C A242270 a(13) >= 720. - _Kevin P. Thompson_, Apr 20 2022 %H A242270 FactorDB, <a href="http://factordb.com/index.php?id=1100000000045034824">Status of 720*7^720+1</a> %t A242270 Select[Range[80], PrimeOmega[# 7^# + 1] == 2 &] %o A242270 (Magma) IsSemiprime:=func<i | &+[d[2]: d in Factorization(i)] eq 2>; [n: n in [1..80] | IsSemiprime(s) where s is n*7^n+1]; %o A242270 (PARI) is(k) = bigomega(k*7^k+1)==2; %o A242270 for(k=0,120,if(k%4!=1,if(is(k),print1(k, ", ")))); \\ _Jinyuan Wang_, Apr 07 2019 %Y A242270 Cf. similar sequences listed in A242203. %Y A242270 Cf. A050919, A242177. %K A242270 nonn,more %O A242270 1,1 %A A242270 _Vincenzo Librandi_, May 10 2014 %E A242270 a(7)-a(9) from _Jinyuan Wang_, Apr 07 2019 %E A242270 a(10)-a(12) from _Kevin P. Thompson_, Apr 20 2022