OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
tri[n_] := n (n + 1)/2; triRoot[n_] := (-1 + Sqrt[8 n + 1])/2; triQ[n_] := IntegerQ @ Sqrt[8 n + 1]; f[n_] := Module[{k = triRoot[n] + 1}, While[!triQ[ GCD[n, (t = tri[k])]], k++]; t]; s = {1}; Nest[AppendTo[s, f[s[[-1]]]] &, s, 48] (* Amiram Eldar, Dec 23 2019 *)
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Jason Earls, May 18 2004
EXTENSIONS
Better description from Stefan Steinerberger, Feb 07 2006
STATUS
approved