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%I #13 Jan 27 2019 20:57:09
%S 1,1,2,4,5,10,11,22,23,25,26,52,53,106,107,109,110,220,221,442,443,
%T 445,446,892,893,898,899,901,902,1804,1805,3610,3611,3613,3614,3619,
%U 3620,7240,7241,7243,7244,14488,14489,28978,28979,28981,28982,57964,57965
%N a(1)=a(2)=1. a(n+1) = a(n) + a(smallest prime dividing n).
%H Giovanni Resta, <a href="/A128216/b128216.txt">Table of n, a(n) for n = 1..10000</a>
%e The smallest prime dividing 12 is 2. So a(13) = a(12) + a(2) = 52 + 1 = 53.
%p with(numtheory): a[1]:=1:a[2]:=1:for n from 2 to 55 do a[n+1]:=a[n]+a[factorset(n)[1]] od: seq(a[n],n=1..55); # _Emeric Deutsch_, Mar 07 2007
%t a128216[1] = 1; a128216[2] = 1;
%t a128216[n_] := a128216[n] = a128216[n-1] + a128216[First[First[FactorInteger[n-1]]]];
%t Array[a128216, 49] (* data *) (* _Hartmut F. W. Hoft_, Mar 08 2017 *)
%Y Cf. A128215, A020639.
%K nonn
%O 1,3
%A _Leroy Quet_, Feb 19 2007
%E More terms from _Emeric Deutsch_, Mar 07 2007