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 A383816 #15 Jun 22 2025 22:05:46
%S A383816 373,1793971,7933397,374636473,714707417,727939727,787333787,
%T A383816 790585097,947939749,991999199,10253935201,11365556311,11932823911,
%U A383816 13127372131,34390609343,35369996353,35381318353,36297179263,37018281073,37423332473,37773537773,38233333283,38914541983,39064546093
%N A383816 Palindromic primes which satisfy the requirements of A380943 in at least two ways.
%C A383816 Terms of A380943 are primes whose decimal representation is the concatenation of primes p and q such that the concatenation of q and p also forms a prime.
%e A383816 The palindromic prime 373 meets the requirements of A380943 in two ways: the concatenation of 3 and 37 forms the prime 337, and the concatenation of 73 and 3 forms the prime 733.
%e A383816 Although 37673 is a palindrome where 3, 7673, and 76733 are all primes and 3767, 3, and 33767 are all primes, the palindrome is not prime and is therefore not in the sequence.
%t A383816 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]; fQ[n_] := Reverse[idn = IntegerDigits@ n] == idn && f@ n > 1; Select[ Prime@ Range@ 3000000, fQ]
%Y A383816 Subsequence of A383810.
%Y A383816 Cf. A000040, A002385, A105184, A380943.
%K A383816 base,nonn
%O A383816 1,1
%A A383816 _James C. McMahon_ and _Robert G. Wilson v_, Jun 09 2025