%I A007497 M0581
%S A007497 2,3,4,7,8,15,24,60,168,480,1512,4800,15748,28672,65528,122880,
%T A007497 393192,1098240,4124736,15605760,50328576,149873152,371226240,
%U A007497 1710858240,7926750720,33463001088,109760857440,384120963072
%N A007497 a(n) = sigma(a(n-1)).
%D A007497 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, 
               Academic Press, 1995 (includes this sequence).
%H A007497 T. D. Noe, <a href="b007497.txt">Table of n, a(n) for n=1..200</a>
%F A007497 Conjecture : (1/2)*log(n)<a(n+1)/a(n)<2*log(n) - Benoit Cloitre (benoit7848c(AT)orange.fr), 
               May 08 2003
%p A007497 A007497 := proc(n) options remember; if n <= 0 then RETURN(2) else sigma(A007497(n-1)); 
               fi; end;
%t A007497 a[1] = 2; a[n_] := DivisorSigma[1, a[n - 1]]; Table[ a[n], {n, 1, 30} 
               ]
%Y A007497 Cf. A000005.
%Y A007497 Sequence in context: A120611 A092063 A126850 this_sequence A126882 A006549 
               A159554
%Y A007497 Adjacent sequences: A007494 A007495 A007496 this_sequence A007498 A007499 
               A007500
%K A007497 nonn,easy,nice
%O A007497 1,1
%A A007497 N. J. A. Sloane (njas(AT)research.att.com), Robert G. Wilson v (rgwv(AT)rgwv.com)