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 A275285 #14 May 02 2024 04:26:08 %S A275285 1,2,5,6,30,58,66,127,138,179,287,520,767,954,966,1254,1313,1976,2266, %T A275285 2496,3137,4058,4411,7009,11736,12155,21328,31124,31589,38581,42683, %U A275285 54634,56634,85297 %N A275285 Numbers k such that 33*10^k + 7 is prime. %C A275285 For k > 0, numbers k such that the digits 33 followed by k-1 occurrences of the digit 0 followed by the digit 7 is prime (see Example section). %C A275285 a(35) > 10^5. %H A275285 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A275285 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 330w7</a>. %e A275285 5 is in this sequence because 33*10^5 + 7 = 3300007 is prime. %e A275285 Initial terms and associated primes: %e A275285 a(1) = 1, 337; %e A275285 a(2) = 2, 3307; %e A275285 a(3) = 5, 3300007; %e A275285 a(4) = 6, 33000007; %e A275285 a(5) = 30, 33000000000000000000000000000007, etc. %t A275285 Select[Range[0, 100000], PrimeQ[33*10^# + 7] &] %o A275285 (PARI) lista(nn) = for(n=1, nn, if(ispseudoprime(33*10^n+7), print1(n, ", "))); \\ _Altug Alkan_, Jul 21 2016 %Y A275285 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A275285 nonn,more %O A275285 1,2 %A A275285 _Robert Price_, Jul 21 2016