A120637 Primes such that their triple is 2 away from a prime number.

3, 5, 7, 11, 13, 17, 19, 23, 29, 37, 43, 47, 53, 59, 61, 67, 71, 79, 83, 89, 97, 103, 113, 127, 137, 139, 149, 163, 167, 173, 181, 191, 193, 197, 199, 211, 227, 233, 239, 251, 257, 263, 269, 271, 277, 293, 307, 313, 317, 331, 337, 347, 349, 353, 367, 373, 383

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.

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..57.

Formula

Union of A023208 and A088878.

Example

19 is a prime and 19*3 = 57 which is two away from 59 which is prime.
31 is not in the table because 31*3 = 93 which is 2 away from 91 and 95, both not prime.

Mathematica

Select[Prime[Range[200]], PrimeQ[3#+2]||PrimeQ[3#-2]&] (* Harvey P. Dale, Aug 10 2011 *)

Prog

(PARI) primepm2(n, k) { 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. A125272.

Sequence in context: A130057 A226181 A363286 * A278454 A378018 A064534

Adjacent sequences: A120634 A120635 A120636 * A120638 A120639 A120640

Keyword

easy,nonn

Author

Cino Hilliard, Aug 17 2006

Status

approved