A118725 Chen primes for which the reversal is also a Chen prime.

2, 3, 5, 7, 11, 13, 17, 31, 71, 101, 107, 113, 131, 149, 157, 167, 179, 181, 191, 199, 311, 347, 353, 359, 389, 701, 743, 751, 761, 787, 797, 919, 941, 953, 971, 983, 991, 1009, 1031, 1061, 1091, 1097, 1109, 1151, 1217, 1229, 1259, 1283, 1301, 1409, 1439

Offset: 1

Author

Luc Stevens (lms022(AT)yahoo.com), May 21 2006

Keywords

• base
• nonn
• less

Examples

			17 and its reversal 71 are both Chen primes.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A109611.

Programs

Maple

revdigs:= proc(n) local L,k;
  L:= convert(n,base,10);
  add(L[-k]*10^(k-1),k=1..nops(L))
end proc:
filter:= proc(n) local r;
  if not isprime(n) then return false fi;
  r:= revdigs(n);
  isprime(r) and numtheory:-bigomega(n+2) <= 2 and numtheory:-bigomega(r+2) <= 2
end proc:
select(filter, [2,seq(i,i=3..2000,2)]); # Robert Israel, Jun 16 2020

Mathematica

cpQ[n_]:=Module[{rev=FromDigits[Reverse[IntegerDigits[n]]]}, PrimeOmega[ n+2]<3 && PrimeQ[rev]&&PrimeOmega[rev+2]<3]; Select[Prime[ Range[ 400]], cpQ] (* Harvey P. Dale, Jul 17 2011 *)

Extensions

Corrected by Harvey P. Dale, Jul 17 2011