%I A082449
%S A082449 2,3,7,23,47,283,719,1439,2879,34549,138197,1266767,14619833,36449279,
%T A082449 377982107,1432349099,22111003847
%N A082449 Let f(p) = greatest prime divisor of p-1. Sequence gives smallest prime 
               which takes at least n steps to reach 2 when f is iterated.
%C A082449 There is a remarkable and unexplained agreement: if 3 and 7 are replaced 
               by 11 and 14619833 is replaced by 14920303, the result is sequence 
               A056637 (least prime of class n-, according to the Erdos-Selfridge 
               classification of primes).
%D A082449 Steven G. Johnson, Postings to Number Theory List, Apr 23 and Apr 25, 
               2003.
%e A082449 a(2) = 7 since 7 -> 3 -> 2 takes two steps; for p = 2879, 8 steps are 
               needed (2879 -> 1439 -> 719 -> 359 -> 179 -> 89 -> 11 -> 5 -> 2), 
               so a(8) = 2879; smaller primes require less than 2 resp. 8 steps.
%Y A082449 Cf. A006530, A023503, A083647, A056637, A083647.
%Y A082449 Sequence in context: A106865 A000057 A037231 this_sequence A129741 A006720 
               A084710
%Y A082449 Adjacent sequences: A082446 A082447 A082448 this_sequence A082450 A082451 
               A082452
%K A082449 nonn,more
%O A082449 0,1
%A A082449 N. J. A. Sloane (njas(AT)research.att.com), Apr 25 2003
%E A082449 Edited by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de), May 01 2003
%E A082449 a(16) from Donovan Johnson (donovan.johnson(AT)yahoo.com), Nov 17 2008