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A081973 a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.

%I A081973 #24 Feb 23 2024 07:26:14
%S A081973 1,2,5,11,23,47,95,215,479,959,2063,4127,8255,19007,38327,76655,
%T A081973 168647,338663,708263,1453823,3308543,7154303,14919599,29910119,
%U A081973 59820239,119676959,239387375,538142975,1205440295,2651968655,6663140495
%N A081973 a(1) = 1; a(n) = a(n-1) + sigma(a(n-1)) where sigma(k) = sum of the divisors of k.
%C A081973 a(n+1)/a(n) >= 2 for all n. Is a(n+1)/a(n) bounded? Up to n=160, the maximum value is a(31)/a(30)=2.5125261124174184479... - _Benoit Cloitre_, Apr 17 2003
%C A081973 a(n) == 23 (mod 24) for all n>=5. - _Dean Hickerson_, Apr 20 2003
%C A081973 a(n) = partial sums of A165929(n). [From _Jaroslav Krizek_, Sep 30 2009]
%H A081973 T. D. Noe, <a href="/A081973/b081973.txt">Table of n, a(n) for n=1..200</a>
%t A081973 a[1]=1; a[n_] := a[n]=a[n-1]+DivisorSigma[1, a[n-1]]
%K A081973 nonn
%O A081973 1,2
%A A081973 _Amarnath Murthy_, Apr 03 2003
%E A081973 More terms from Gabriel Cunningham (gcasey(AT)mit.edu), Apr 07 2003