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a(n) = a(n-1) + largest divisor of a(n-1) <= sqrt(a(n-1)).
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%I #9 Sep 16 2015 13:15:03

%S 1,2,3,4,6,8,10,12,15,18,21,24,28,32,36,42,48,54,60,66,72,80,88,96,

%T 104,112,120,130,140,150,160,170,180,192,204,216,228,240,255,270,285,

%U 300,315,330,345,360,378,396,414,432,450,468,486,504,525,546,567,588,609

%N a(n) = a(n-1) + largest divisor of a(n-1) <= sqrt(a(n-1)).

%H Harvey P. Dale, <a href="/A139542/b139542.txt">Table of n, a(n) for n = 1..1000</a>

%e Term after 36 is 42 because largest divisor of 36 <= sqrt(36) is 6 and 36+6=42

%t a = {1}; Do[AppendTo[a, a[[ -1]] + Max[Select[Divisors[a[[ -1]]], # <= Sqrt[a[[ -1]]] &]]], {60}]; a (* _Stefan Steinerberger_, Aug 28 2008 *)

%t ld[n_]:=Max[Select[Divisors[n],#<=Sqrt[n]&]]; NestList[#+ld[#]&,1,60] (* _Harvey P. Dale_, Nov 26 2011 *)

%K nonn

%O 1,2

%A _J. Lowell_, Jun 10 2008

%E More terms from _Stefan Steinerberger_, Aug 28 2008