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

1,1

Links

Table of n, a(n) for n=1..50.

Example

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

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 *)

Crossrefs

Cf. A109611.

Sequence in context: A117159 A134873 A172979 * A055387 A046732 A293663

Adjacent sequences: A118721 A118722 A118723 * A118725 A118726 A118727

Keyword

base,nonn

Author

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

Extensions

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

Status

approved