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
Keywords
Examples
977 is prime, 976 = 2^4*61 and 975 = 3*5^2*13 are not semiprimes, 974 = 2*487 is a semiprime.
Links
- T. D. Noe, Table of n, a(n) for n = 1..1000
Crossrefs
Cf. A217195.
Programs
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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 *)
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PARI
forprime(p=5, 9999, bigomega(p-3)==2 && bigomega(p-1)!=2 && bigomega(p-2)!=2 & print1(p", "))
Comments