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A117242 Chen primes that are not members of twin primes. 1

%I #8 May 13 2013 01:54:08

%S 2,23,37,47,53,67,83,89,113,127,131,157,167,211,233,251,257,263,293,

%T 307,317,337,353,359,379,389,401,409,443,449,467,479,487,491,499,503,

%U 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

%N Chen primes that are not members of twin primes.

%H Charles R Greathouse IV, <a href="/A117242/b117242.txt">Table of n, a(n) for n = 1..10000</a>

%e 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.

%p 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:

%p 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:

%p ts_chen_non_twin_primes(1000);

%o (PARI) is(n)=isprime(n)&&bigomega(n+2)==2&&!isprime(n-2) \\ _Charles R Greathouse IV_, May 04 2013

%Y Cf. A001097, A109611.

%K nonn

%O 1,1

%A _Jani Melik_, Apr 22 2006

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Last modified March 19 02:58 EDT 2024. Contains 370952 sequences. (Running on oeis4.)