

A321420


Primes p whose reversal is a Chen prime.


0



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
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OFFSET

1,1


COMMENTS

73 is the smallest nonChen 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



