A321420 Primes p whose reversal is a Chen prime.

2, 3, 5, 7, 11, 13, 17, 31, 71, 73, 101, 107, 113, 131, 149, 157, 167, 179, 181, 191, 199, 311, 347, 353, 359, 389, 701, 733, 739, 743, 751, 761, 787, 797, 919, 941, 953, 967, 971, 983, 991, 1009, 1021, 1031, 1061, 1091, 1097, 1103, 1109, 1151, 1153, 1217, 1223

Offset: 1

Author

Paolo Galliani, Nov 09 2018

Keywords

• nonn
• base

Comments

73 is the smallest non-Chen prime whose reversal is a Chen prime.

Examples

			73 is in the sequence because its reversal is 37 which is a Chen prime (because 37 + 2 = 39 has at most two prime factors).
		

Crossrefs

Cf. A118725, A109611, A102540.

Programs

Mathematica

cpQ[n_] := Module[{rev = FromDigits[Reverse[IntegerDigits[n]]]}, PrimeQ[rev] && PrimeOmega[rev + 2] < 3]; Select[Prime[Range[400]], cpQ] (* Amiram Eldar, Nov 09 2018 after Harvey P. Dale at A118725 *)

PARI

is(n) = if(isprime(n), rn = fromdigits(Vecrev(digits(n))); return(isprime(rn) && bigomega(rn+2) <= 2), 0) \\ David A. Corneth, Nov 09 2018