A321422 Primes that are non-Chen primes whose reversal is a Chen prime.

73, 733, 739, 967, 1021, 1103, 1153, 1223, 1237, 1453, 1523, 1657, 1723, 1741, 1831, 3023, 3911, 7057, 7187, 7523, 7577, 7643, 7673, 7699, 7717, 7841, 9161, 9173, 9293, 9497, 9679, 9749, 9803, 9833, 9883, 9923, 9931, 10151, 10273, 10453, 10853, 11003, 11083, 11243, 11423

Offset: 1

Author

Paolo Galliani, Nov 09 2018

Keywords

• nonn
• base

Comments

The second term of the sequence: 733 is congruent to 1 mod 61, to 2 mod 43, to 3 mod 73, where 61 is the second non-Chen prime, 43 is the first non-Chen prime and 73 is the third non-Chen prime. 733 is also congruent to 4 mod (3^6).

Crossrefs

Cf. A109611, A102540.

Programs

Mathematica

cpQ[n_] := Module[{rev = FromDigits[Reverse[IntegerDigits[n]]]}, PrimeOmega[n + 2] > 2 && PrimeQ[rev] && PrimeOmega[rev + 2] < 3]; Select[Prime[Range[1300]], cpQ] (* Amiram Eldar, Nov 09 2018 after Harvey P. Dale at A118725 *)

PARI

forprime(p=1,10^4,w=Vecrev(digits(p));q=0;for(j=1,length(w),q=q*10+w[j]);if(ispseudoprime(q)==1,if(bigomega(p+2)>2,if(bigomega(q+2)<=2,print1(p,", ")))))