1,1

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

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.

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 *)

Cf. A109611.

Sequence in context: A293663 A317688 A046703 * A051026 A028865 A053435

Adjacent sequences: A118719 A118720 A118721 * A118723 A118724 A118725

base,nonn

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

approved