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A139422 a(1)=a(2)=1. For n >= 3, a(n) = a(n-1) + d(a(n-1)) + d(a(n-2)), where d(m) is the number of positive divisors of m.

%I A139422 #11 Feb 06 2019 00:46:20
%S A139422 1,1,3,6,12,22,32,42,56,72,92,110,124,138,152,168,192,222,244,258,272,
%T A139422 290,308,328,348,368,390,416,444,468,498,524,538,548,558,576,609,638,
%U A139422 654,670,686,702,726,754,774,794,810,834,862,874
%N A139422 a(1)=a(2)=1. For n >= 3, a(n) = a(n-1) + d(a(n-1)) + d(a(n-2)), where d(m) is the number of positive divisors of m.
%p A139422 with(numtheory): a[1]:=1: a[2]:=1: for n from 3 to 50 do a[n]:=a[n-1]+tau(a[n-1])+tau(a[n-2]) end do: seq(a[n],n=1..50); # _Emeric Deutsch_, Apr 26 2008
%t A139422 Join[{a = 1, b = 1}, Table[c = b + Total[DivisorSigma[0, {a, b}]]; a = b; b = c; c, {n, 48}]] (* _Jayanta Basu_, Jun 06 2013 *)
%Y A139422 Cf. A139423, A064491.
%K A139422 nonn
%O A139422 1,3
%A A139422 _Leroy Quet_, Apr 21 2008
%E A139422 More terms from _Emeric Deutsch_, Apr 26 2008