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 A272402 #16 May 02 2024 04:23:51 %S A272402 1,2,3,5,7,10,15,20,31,107,115,290,455,611,669,1190,2111,2147,2821, %T A272402 4094,4616,7087,7971,11416,12413,21475,23719,24435,32218,122625, %U A272402 160166,190789 %N A272402 Numbers k such that (26*10^k - 131)/3 is prime. %C A272402 For k > 1, numbers k such that the digit 8 followed by k-2 occurrences of the digit 6 followed by the digits 23 is prime (see Example section). %C A272402 a(33) > 2*10^5. %H A272402 Makoto Kamada, <a href="https://stdkmd.net/nrr">Factorization of near-repdigit-related numbers</a>. %H A272402 Makoto Kamada, <a href="https://stdkmd.net/nrr/prime/prime_difficulty.txt">Search for 86w23</a>. %e A272402 3 is in this sequence because (26*10^3 - 131)/3 = 8623 is prime. %e A272402 Initial terms and associated primes: %e A272402 a(1) = 1, 43; %e A272402 a(2) = 2, 823; %e A272402 a(3) = 3, 8623; %e A272402 a(4) = 5, 866623; %e A272402 a(5) = 7, 86666623, etc. %t A272402 Select[Range[0, 100000], PrimeQ[(26*10^# - 131)/3] &] %o A272402 (PARI) isok(n) = isprime((26*10^n - 131)/3); \\ _Michel Marcus_, Apr 28 2016 %Y A272402 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A272402 nonn,more %O A272402 1,2 %A A272402 _Robert Price_, Apr 28 2016 %E A272402 a(30)-a(32) from _Robert Price_, Oct 19 2019