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A117242 Chen primes that are not members of twin primes. 1
2, 23, 37, 47, 53, 67, 83, 89, 113, 127, 131, 157, 167, 211, 233, 251, 257, 263, 293, 307, 317, 337, 353, 359, 379, 389, 401, 409, 443, 449, 467, 479, 487, 491, 499, 503, 509, 541, 557, 563, 577, 587, 631, 647, 653, 677, 683, 701, 719, 743, 751, 761, 769, 787, 797, 839, 863, 877, 887, 911, 919, 937, 941, 947, 953, 971, 977, 983, 991 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

a(1) = 2, 2 is Chen number but not member of twin primes, a(2) = 23 is Chen number, but not member of twin primes.

MAPLE

ischenprime:=proc(n); if (isprime(n) = 'true') then if (isprime(n+2) = 'true' or numtheory[bigomega](n+2) = 2) then RETURN('true') else RETURN('false') fi fi end:

ts_chen_non_twin_primes:=proc(n) local i, ans; ans:=[ ]: for i from 1 to n do if (ischenprime(i) = 'true') and (isprime(i+2) = 'false' and isprime(i-2) = 'false') then ans:=[op(ans), i]: fi od; RETURN(ans) end:

ts_chen_non_twin_primes(1000);

PROG

(PARI) is(n)=isprime(n)&&bigomega(n+2)==2&&!isprime(n-2) \\ Charles R Greathouse IV, May 04 2013

CROSSREFS

Cf. A001097, A109611.

Sequence in context: A049580 A061448 A007510 * A144550 A106736 A045392

Adjacent sequences:  A117239 A117240 A117241 * A117243 A117244 A117245

KEYWORD

nonn

AUTHOR

Jani Melik, Apr 22 2006

STATUS

approved

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Last modified January 22 23:00 EST 2019. Contains 319365 sequences. (Running on oeis4.)