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A118723 Chen primes for which the digital root is also a Chen prime. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified April 26 04:55 EDT 2019. Contains 322469 sequences. (Running on oeis4.)