A118724 Chen primes for which the multiplicative digital root is also a Chen prime.

2, 3, 5, 7, 13, 17, 31, 37, 53, 71, 113, 131, 137, 157, 211, 311, 317, 359, 389, 431, 557, 571, 751, 827, 839, 953, 983, 1117, 1151, 1297, 1367, 1511, 1553, 1621, 1637, 1759, 2111, 2179, 2213, 2269, 2339, 2393, 2699, 2719, 2969, 2971, 3167, 3221, 3329, 3511

Offset: 1

Author

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

Keywords

• base
• nonn

Examples

			157 is in the sequence because (1) it is a Chen prime and (2) the multiplicative digital root 5 is also a Chen prime.
		

Crossrefs

Cf. A109611.

Programs

Mathematica

mdr[n_] := NestWhile[Times @@ IntegerDigits@# &, n, # > 9 &]; chenQ[n_] := PrimeQ[n] && Plus @@ Last /@ FactorInteger[n + 2] < 3; Select[ Prime@ Range@500, chenQ@ mdr@# && chenQ@# &] (* Robert G. Wilson v *)

Extensions

More terms from Robert G. Wilson v, May 22 2006