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 A088884 #15 Jun 08 2025 16:15:42 %S A088884 3,5,11,53,107,131,149,167,179,191,311,317,389,503,599,947,971,1049, %T A088884 1061,1097,1187,1223,1259,1427,1439,1523,1571,1583,1697,1721,1787, %U A088884 1811,1871,1913,1931,1949,3089,3119,3191,3209,3299,3449,3617,3671,3677,3761 %N A088884 Primes which when concatenated with their reverse and decremented by 2 yield a new prime. %C A088884 It appears that if concat(p,reverse(p))-2 is prime, then concat(p,reverse(p))+2 is not and vice versa. This was tested for the first 60000 primes. %C A088884 Conjecture: except for 3, all these primes are of the form 6*k - 1. - _Davide Rotondo_, Apr 29 2025 %H A088884 Harvey P. Dale, <a href="/A088884/b088884.txt">Table of n, a(n) for n = 1..1000</a> %e A088884 53 is a term because (i) 53 is prime and (ii) when 53 is concatenated with its reverse (35) - 2, the result (5333) is prime. %t A088884 Select[Prime[Range[600]],PrimeQ[FromDigits[Join[IntegerDigits[#], Reverse[ IntegerDigits[ #]]]]- 2]&] (* _Harvey P. Dale_, Apr 06 2017 *) %Y A088884 Cf. A067087 (concatenation of n-th prime and its reverse), A088883 (with incremented rather than decremented). %K A088884 base,nonn %O A088884 1,1 %A A088884 _Chuck Seggelin_, Oct 21 2003