A005110 Class 2- primes (for definition see A005109). (Formerly M4783)

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

1,1

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

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 *)

Crossrefs

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

Sequence in context: A196357 A196360 A072711 * A059337 A126240 A124110

Adjacent sequences: A005107 A005108 A005109 * A005111 A005112 A005113

Keyword

nonn

Author

N. J. A. Sloane, Simon Plouffe

Extensions

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

Corrected by R. J. Mathar, Feb 01 2007

Status

approved