A217195 Primes p such that p-2 is the greatest semiprime less than p.

17, 37, 41, 53, 67, 71, 79, 89, 97, 113, 131, 157, 163, 211, 223, 239, 251, 269, 293, 307, 311, 331, 337, 367, 373, 379, 397, 409, 419, 439, 449, 487, 491, 499, 521, 547, 593, 599, 613, 631, 673, 683, 691, 701, 709, 733, 739, 751, 757, 769, 773, 787, 809

Offset

1,1

Comments

This is a subsequence of A063638.

Links

T. D. Noe, Table of n, a(n) for n = 1..1000

Example

487 is prime, 486 = 2*3^5 is not semiprime and 485 = 5*97 is semiprime.

Mathematica

SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Prime[Range[200]], ! SemiPrimeQ[# - 1] && SemiPrimeQ[# - 2] &] (* T. D. Noe, Sep 27 2012 *)

Prog

(PARI) forprime(p=3, 9999, bigomega(p-2)==2 && bigomega(p-1)!=2 & print1(p", "))

Crossrefs

Sequence in context: A190755 A098849 A319059 * A177835 A075698 A165493

Adjacent sequences: A217192 A217193 A217194 * A217196 A217197 A217198

Keyword

nonn

Author

Antonio Roldán, Sep 27 2012

Status

approved