%I A081426
%S A081426 1439,8629,10067,14683,17257,19577,20389,22643,23743,27103,28219,29399,
%T A081426 31657,32633,33107,33113,33863,34259,34513,35951,36137,36887,37379,
%U A081426 40127,40637,40759,42179,42209,42767,44519,44579,45139,49019,49669
%N A081426 Class 7- primes.
%D A081426 R. K. Guy, Unsolved Problems in Number Theory, A18.
%H A081426 R. J. Mathar, <a href="b081426.txt">Table of n, a(n) for n = 1..20000</
               a>
%t A081426 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[5200], ClassMinusNbr[ Prime[ # ]] == 7 
               &]]
%Y A081426 Cf. A005113, A056637, A005109, A005110, A005111, A005112, A081424, A081425, 
               A081427, A081428, A081429, A081430.
%Y A081426 Sequence in context: A127491 A143475 A101798 this_sequence A101998 A063846 
               A078095
%Y A081426 Adjacent sequences: A081423 A081424 A081425 this_sequence A081427 A081428 
               A081429
%K A081426 nonn
%O A081426 1,1
%A A081426 Robert G. Wilson v (rgwv(AT)rgwv.com), Mar 20 2003