A005110 Class 2- primes (for definition see A005109).

11, 29, 31, 41, 43, 53, 61, 71, 79, 101, 103, 113, 127, 131, 137, 149, 151, 157, 181, 191, 197, 211, 223, 229, 239, 241, 251, 271, 281, 293, 307, 313, 337, 379, 389, 401, 409, 421, 439, 443, 449, 457, 491, 521, 541, 547, 571, 593, 601, 613, 631, 641, 647, 653, 673

Offset: 1

Author

N. J. A. Sloane, Simon Plouffe

Keywords

• nonn

References

• R. K. Guy, Unsolved Problems in Number Theory, A18.
• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• R. J. Mathar, Table of n, a(n) for n = 1..13766

Crossrefs

Cf. A005113, A056637, A005109, A005111, A005112, A081424, A081425, A081426, A081427, A081428, A081429, A081430.

Programs

Mathematica

PrimeFactors[n_Integer] := Flatten[ Table[ #[[1]], {1}] & /@ FactorInteger[n]];
f[n_Integer] := Block[{m = n}, If[m == 0, m = 1, While[ IntegerQ[m/2], m /= 2];
While[ IntegerQ[m/3], m /= 3]];
Apply[Times, PrimeFactors[m] - 1]];
ClassMinusNbr[n_] := Length[NestWhileList[f, n, UnsameQ, All]] - 3;
Prime[ Select[ Range[122], ClassMinusNbr[ Prime[ # ]] == 2 &] ] (* Robert G. Wilson v *)

Extensions

Edited and extended by Robert G. Wilson v, Mar 20 2003

Corrected by R. J. Mathar, Feb 01 2007