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A217197 Primes p such that p-3 is the greatest semiprime less than p. 1
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified December 14 17:32 EST 2019. Contains 329979 sequences. (Running on oeis4.)