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A005107 Class 3+ primes (for definition see A005105).
(Formerly M5261)
21

%I M5261

%S 37,103,113,151,157,163,173,181,193,227,233,257,277,311,331,337,347,

%T 353,379,389,397,401,409,421,457,463,467,487,491,521,523,541,547,569,

%U 571,601,607,613,631,653,683,701,727,733,773,787,797,811,821,829,853,857

%N Class 3+ primes (for definition see A005105).

%D R. K. Guy, Unsolved Problems in Number Theory, A18.

%D N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

%H T. D. Noe, <a href="/A005107/b005107.txt">Table of n, a(n) for n=1..10000</a>

%p For Maple program see Mathar link in A005105.

%t 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]]; ClassPlusNbr[n_] := Length[ NestWhileList[f, n, UnsameQ, All]] - 3; Prime[ Select[ Range[150], ClassPlusNbr[ Prime[ # ]] == 3 &]]

%Y Cf. A005113, A005105, A005106, A005108.

%K nonn

%O 1,1

%A _N. J. A. Sloane_, _Simon Plouffe_

%E Edited and extended by _Robert G. Wilson v_, Mar 20 2003

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Last modified May 20 03:10 EDT 2019. Contains 323412 sequences. (Running on oeis4.)