A120638 Primes such that their triple is not 2 away from a prime number.

2, 31, 41, 73, 101, 107, 109, 131, 151, 157, 179, 223, 229, 241, 281, 283, 311, 359, 379, 389, 421, 449, 463, 509, 521, 547, 563, 571, 599, 613, 617, 619, 631, 641, 647, 653, 661, 683, 691, 701, 719, 733, 739, 743, 773, 787, 809, 811, 821, 827, 829, 839, 857

Offset

1,1

Comments

This sequence is a variation of the sequence in the reference. However, this sequence should have an infinite number of terms. k=2 in the PARI code.

References

R. Crandall and C. Pomerance, Prime Numbers A Computational Perspective, Springer Verlag 2002, p. 49, exercise 1.18.

Links

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

Example

31*3 = 93 which is two away from 91 and 95 both not prime.

Mathematica

Select[Prime@Range@200, !PrimeQ[3#-2]&&!PrimeQ[3#+2]&] (* Vladimir Joseph Stephan Orlovsky, Apr 25 2011 *)
Select[Prime[Range[200]], NoneTrue[3#+{2, -2}, PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Feb 01 2019 *)

Prog

(PARI) primepm3(n, k) = =number of iterations, k = factor { local(x, p1, p2, f1, f2, r); if(k%2, r=2, r=1); for(x=1, n, p1=prime(x); p2=prime(x+1); if(!isprime(p1*k+r)&!isprime(p1*k-r), print1(p1", ") ) ) }

Crossrefs

Cf. A023208, A088878, A125272.

Sequence in context: A102630 A264783 A215031 * A101017 A207973 A193423

Adjacent sequences: A120635 A120636 A120637 * A120639 A120640 A120641

Keyword

easy,nonn

Author

Cino Hilliard, Aug 17 2006

Status

approved