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 A273097 #22 May 26 2024 14:28:42 %S A273097 1,2,4,5,13,25,27,32,37,38,40,45,57,80,91,151,214,441,644,764,797, %T A273097 1222,2329,2931,4324,21794,22396,24041,46420,51489,55165,126625 %N A273097 Numbers k such that 4*10^k + 87 is prime. %C A273097 For k > 1, numbers k such that the digit 4 followed by k-2 occurrences of the digit 0 followed by the digits 87 is prime (see Example section). %C A273097 a(33) > 3*10^5. %H A273097 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A273097 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 40w87</a>. %e A273097 4 is in this sequence because 4*10^4 + 87 = 40087 is prime. %e A273097 Initial terms and associated primes: %e A273097 a(1) = 1, 127: %e A273097 a(2) = 2, 487; %e A273097 a(3) = 4, 40087; %e A273097 a(4) = 5, 400087; %e A273097 a(5) = 13, 40000000000087, etc. %t A273097 Select[Range[0, 100000], PrimeQ[4*10^# + 87] &] %o A273097 (PARI) is(n)=ispseudoprime(4*10^n + 87) \\ _Charles R Greathouse IV_, Jun 13 2017 %Y A273097 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A273097 nonn,more %O A273097 1,2 %A A273097 _Robert Price_, May 15 2016 %E A273097 a(32) from _Robert Price_, Aug 15 2018