A181841 Supersafe primes.

7, 11, 23, 59, 179, 383, 503, 719, 1319, 1439, 1823, 2579, 2903, 3119, 3779, 4283, 4679, 4703, 5099, 5639, 5939, 6719, 8783, 8819, 10079, 12659, 12983, 13523, 15299, 15683, 16223, 17483, 18743, 19079, 21059, 21383, 21563, 22643, 23099, 23603, 24659, 25343

Offset: 1

Author

Peter Luschny, Nov 17 2010

Keywords

• nonn

Comments

p is a supersafe prime iff p is a safe prime (A005385) and floor(p/3) is a prime.

Each prime p > 7 is preceded by two semiprimes; a third semiprime is not possible. See A036570. - Zak Seidov, Sep 30 2012

Terms > 7 are congruent to 11 (mod 12). - Zak Seidov, Feb 09 2015

Examples

			11 is a supersafe prime because floor(11/2) = 5 and floor(11/3) = 3 are primes.
		

Links

• Zak Seidov, Table of n, a(n) for n = 1..2000
• Peter Luschny, Strong coprimality.

Crossrefs

Cf. A005385, A036570.

Programs

Maple

A181841_list := n->select(i->isprime(iquo(i,3)),
select(i->isprime(iquo(i,2)), select(i->isprime(i),[$1..n]))):

Mathematica

Join[{7}, Select[Table[Prime[n], {n, 4000}], PrimeQ[(# - 1)/2] && PrimeQ[(# - 2)/3] &]] (* Vladimir Joseph Stephan Orlovsky, Jun 21 2011 *)