A118723 Chen primes for which the 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

1,1

Links

Table of n, a(n) for n=1..55.

Example

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

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 *)

Prog

(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

Crossrefs

Cf. A109611.

Sequence in context: A070027 A207294 A156658 * A118721 A094318 A019344

Adjacent sequences: A118720 A118721 A118722 * A118724 A118725 A118726

Keyword

base,nonn

Author

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

Status

approved