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

1,1

Comments

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

Links

Table of n, a(n) for n=1..53.

Example

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).

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 *)

Prog

(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

Crossrefs

Cf. A118725, A109611, A102540.

Sequence in context: A202264 A253717 A186307 * A118725 A117835 A120639

Adjacent sequences: A321417 A321418 A321419 * A321421 A321422 A321423

Keyword

nonn,base

Author

Paolo Galliani, Nov 09 2018

Status

approved