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

1,1

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

Links

Zak Seidov, Table of n, a(n) for n = 1..2000

Peter Luschny, Strong coprimality.

Example

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

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 *)

Crossrefs

Cf. A005385, A036570.

Sequence in context: A118072 A141305 A243916 * A076855 A160054 A359414

Adjacent sequences: A181838 A181839 A181840 * A181842 A181843 A181844

Keyword

nonn

Author

Peter Luschny, Nov 17 2010

Status

approved