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 A297422 #23 Apr 12 2018 02:52:26 %S A297422 0,1,3,5,10,196,251,310,415,1107,2422 %N A297422 Numbers k such that 4*10^(2k) + 2*(10^k) + 1 is prime. %C A297422 Numbers of this form divide 8*(10^3k)-1. %C A297422 a(12) > 50000. - _Robert Price_, Apr 11 2018 %e A297422 7, 421, 4002001, and 40000200001 are prime, while 40201=7*5743, 400020001=31*12903871, etc. %p A297422 select(k->isprime(4*10^(2*k)+2*(10^k)+1),[$0..1000]); # _Muniru A Asiru_, Apr 11 2018 %t A297422 Select[Range[1500], PrimeQ[4 (10^(2 #)) + 2 (10^#) + 1] &] (* _Michael De Vlieger_, Dec 30 2017 *) %o A297422 (PARI) isok(k) = isprime(4*10^(2*k)+2*(10^k)+1); \\ _Michel Marcus_, Dec 30 2017 %K A297422 nonn,more %O A297422 1,3 %A A297422 _Patrick A. Thomas_, Dec 30 2017 %E A297422 a(6)-a(10) from _Michael De Vlieger_, Dec 30 2017 %E A297422 a(11) from _Jon E. Schoenfield_, Jan 01 2018