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 A383813 #14 May 31 2025 14:37:55
%S A383813 257931013,1394821313,2699357347,3122419127,3132143093,3647381953,
%T A383813 3736320359,3799933727,6130099337,7622281937,7943701397,7991407367
%N A383813 Primes which satisfy the requirements of A380943 in exactly four ways.
%C A383813 The requirements of A380943 are that primes, p_n, written in decimal representation by the concatenation of primes p and q such that the concatenation of q and p also forms a prime.
%C A383813 The number of terms <= 10^k beginning with k=1: 0, 0, 0, 0, 0, 0, 0, 1, 12, ..., .
%t A383813 f[n_] := Block[{cnt = 0, id = IntegerDigits@ n, k = 1, len, p, q, qp}, len = Length@ id; While[k < len, p = Take[id, k]; q = Take[id, -len + k]; qp = FromDigits[ Join[q, p]]; If[ PrimeQ[FromDigits[p]] && PrimeQ[FromDigits[q]] && PrimeQ[qp] && IntegerLength[qp] == len, cnt++]; k++]; cnt];Select[ Prime@ Range@ 10000000, f@# == 4 &]
%Y A383813 Cf. A000040, A238500, A380943, A383810, A383811, A383812, A383814, A383815, A383816.
%K A383813 nonn,base,more
%O A383813 1,1
%A A383813 _James C. McMahon_ and _Robert G. Wilson v_, May 23 2025