A118723 Chen primes whose digital root is also a Chen prime.

2, 3, 5, 7, 11, 23, 29, 41, 47, 59, 83, 101, 113, 131, 137, 149, 167, 191, 227, 239, 257, 263, 281, 293, 311, 317, 347, 353, 389, 401, 419, 443, 461, 479, 491, 509, 563, 569, 587, 599, 617, 641, 653, 659, 677, 743, 761, 797, 821, 839, 857, 887, 911, 941, 947

Offset: 1

Author

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

Keywords

• base
• nonn

Examples

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

Crossrefs

Cf. A010888, A109611.

Programs

Mathematica

digitalRoot[n_Integer?Positive] := FixedPoint[Plus@@IntegerDigits[#] &, n];
chenPrimeQ[x_] := PrimeQ[x] && Plus@@Last/@FactorInteger[x+2] <= 2;
Select[Range[1000], chenPrimeQ[#] && chenPrimeQ[digitalRoot[#]]&] (* Vladimir Joseph Stephan Orlovsky, Apr 30 2011, with a function by Eric W. Weisstein *)

PARI

isA118723(n)=[0,0,1,1,0,1,0,1,0][n%9+1]&isprime(n)&bigomega(n+2)<3 \\ Charles R Greathouse IV, Apr 30 2011