A117243 Chen numbers which are also twin primes.

3, 5, 7, 11, 13, 17, 19, 29, 31, 41, 59, 71, 101, 107, 109, 137, 139, 149, 179, 181, 191, 197, 199, 227, 239, 269, 281, 311, 347, 419, 431, 461, 521, 569, 571, 599, 617, 641, 659, 809, 811, 821, 827, 829, 857, 881, 1019, 1031, 1049, 1061, 1091, 1151, 1229

Offset

1,1

Links

Table of n, a(n) for n=1..53.

Example

(3, 5) are twin numbers and also Chen numbers.

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_twin_primes:=proc(n) local i, ans; ans:=[ ]: for i from 1 to n do if (ischenprime(i) = 'true') and (isprime(i+2) = 'true' or isprime(i-2) = 'true') then ans:=[op(ans), i]: fi od; RETURN(ans) end:
ts_chen_twin_primes(1230);

Mathematica

Select[Prime[Range[250]], PrimeOmega[#+2]<3&&AnyTrue[#+{2, -2}, PrimeQ]&] (* Harvey P. Dale, Jul 28 2023 *)

Crossrefs

Cf. A001097, A109611.

Sequence in context: A132143 A239879 A001097 * A179679 A059362 A212376

Adjacent sequences: A117240 A117241 A117242 * A117244 A117245 A117246

Keyword

nonn

Author

Jani Melik, Apr 22 2006

Extensions

Corrected and extended by Jani Melik, May 04 2013

Status

approved