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

%I A005110 M4783 #22 Mar 15 2015 18:51:44
%S A005110 11,29,31,41,43,53,61,71,79,101,103,113,127,131,137,149,151,157,181,
%T A005110 191,197,211,223,229,239,241,251,271,281,293,307,313,337,379,389,401,
%U A005110 409,421,439,443,449,457,491,521,541,547,571,593,601,613,631,641,647,653,673
%N A005110 Class 2- primes (for definition see A005109).
%D A005110 R. K. Guy, Unsolved Problems in Number Theory, A18.
%D A005110 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005110 R. J. Mathar, <a href="/A005110/b005110.txt">Table of n, a(n) for n = 1..13766</a>
%t A005110 PrimeFactors[n_Integer] := Flatten[ Table[ #[[1]], {1}] & /@ FactorInteger[n]];
%t A005110 f[n_Integer] := Block[{m = n}, If[m == 0, m = 1, While[ IntegerQ[m/2], m /= 2];
%t A005110 While[ IntegerQ[m/3], m /= 3]];
%t A005110 Apply[Times, PrimeFactors[m] - 1]];
%t A005110 ClassMinusNbr[n_] := Length[NestWhileList[f, n, UnsameQ, All]] - 3;
%t A005110 Prime[ Select[ Range[122], ClassMinusNbr[ Prime[ # ]] == 2 &] ] (* _Robert G. Wilson v_ *)
%Y A005110 Cf. A005113, A056637, A005109, A005111, A005112, A081424, A081425, A081426, A081427, A081428, A081429, A081430.
%K A005110 nonn
%O A005110 1,1
%A A005110 _N. J. A. Sloane_, _Simon Plouffe_
%E A005110 Edited and extended by _Robert G. Wilson v_, Mar 20 2003
%E A005110 Corrected by _R. J. Mathar_, Feb 01 2007