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 A274700 #17 May 01 2025 05:37:34 %S A274700 1,7,15,21,91,325,465,853,76717 %N A274700 Numbers k such that 7*10^k + 37 is prime. %C A274700 All terms are odd because 7*(9*11+1)^n + 37 is divisible by 11. %C A274700 a(10) > 10^5. - _Michael S. Branicky_, Apr 30 2025 %e A274700 1 is in this sequence because 7*10 + 37 = 107 is prime. %e A274700 3 is not in the sequence because 7*10^3 + 37 = 31*227. %e A274700 Initial terms and associated primes: %e A274700 a(1) = 1: 107; %e A274700 a(2) = 7: 70000037; %e A274700 a(3) = 15: 7000000000000037; %e A274700 a(4) = 21: 7000000000000000000037; %e A274700 etc. %t A274700 Select[Range[0, 3000], PrimeQ[7 10^# + 37] &] %o A274700 (Magma) [n: n in [1..400] | IsPrime(7*10^n+37)]; %o A274700 (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(7*10^n+37), print1(n, ", "))); \\ _Altug Alkan_, Jul 05 2016 %Y A274700 Cf. similar sequences listed in A274676. %K A274700 nonn,more %O A274700 1,2 %A A274700 _Vincenzo Librandi_, Jul 04 2016 %E A274700 Edited by _Bruno Berselli_, Jul 05 2016 %E A274700 a(9) from _Michael S. Branicky_, Apr 28 2025