A217197 Primes p such that p-3 is the greatest semiprime less than p.

13, 29, 61, 109, 137, 149, 181, 197, 229, 257, 277, 281, 317, 349, 389, 401, 457, 461, 541, 557, 569, 617, 677, 761, 797, 821, 929, 937, 977, 1021, 1097, 1129, 1217, 1237, 1289, 1297, 1321, 1481, 1489, 1549, 1597, 1621, 1721, 1777, 1861, 1877, 1997, 2029

Offset

1,1

Comments

Subsequence of A089531.

Links

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

Example

977 is prime, 976 = 2^4*61 and 975 = 3*5^2*13 are not semiprimes, 974 = 2*487 is a semiprime.

Mathematica

SemiPrimeQ[n_Integer] := If[Abs[n] < 2, False, (2 == Plus @@ Transpose[FactorInteger[Abs[n]]][[2]])]; Select[Prime[Range[500]], ! SemiPrimeQ[# - 1] && ! SemiPrimeQ[# - 2] && SemiPrimeQ[# - 3] &] (* T. D. Noe, Sep 27 2012 *)

Prog

(PARI) forprime(p=5, 9999, bigomega(p-3)==2 && bigomega(p-1)!=2 && bigomega(p-2)!=2 & print1(p", "))

Crossrefs

Cf. A217195.

Sequence in context: A065546 A075636 A139838 * A141196 A269785 A123571

Adjacent sequences: A217194 A217195 A217196 * A217198 A217199 A217200

Keyword

nonn

Author

Antonio Roldán, Sep 27 2012

Status

approved