A118722 Chen primes for which the product of the digits is also a Chen prime.

2, 3, 5, 7, 13, 17, 31, 71, 113, 131, 211, 311, 1117, 1151, 1511, 2111, 11117, 11171, 131111, 311111, 511111, 1111151, 1111211, 1111711, 1117111, 11111117, 11111171, 71111111

Offset

1,1

Links

Table of n, a(n) for n=1..28.

Example

31 is in the sequence because (1) it is a Chen prime and (2) the product of its digits 3*1=3 is also a Chen prime.

Mathematica

chenQ[n_]:=Module[{pidn=Times@@IntegerDigits[n]}, PrimeQ[pidn]&&PrimeOmega[ pidn+2]<3]; With[{chen=Select[Prime[Range[4200000]], PrimeOmega[#+2]<3&]}, Select[chen, chenQ]] (* Harvey P. Dale, Apr 22 2012 *)

Crossrefs

Cf. A109611.

Sequence in context: A293663 A317688 A046703 * A051026 A028865 A053435

Adjacent sequences: A118719 A118720 A118721 * A118723 A118724 A118725

Keyword

base,nonn

Author

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

Status

approved