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A181841 Supersafe primes. 4
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 (list; graph; refs; listen; history; text; internal format)
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
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
Sequence in context: A118072 A141305 A243916 * A076855 A160054 A359414
KEYWORD
nonn
AUTHOR
Peter Luschny, Nov 17 2010
STATUS
approved

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Last modified February 23 06:27 EST 2024. Contains 370267 sequences. (Running on oeis4.)