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%I #9 Sep 27 2019 12:39:11
%S 1,2,2,4,2,6,6,6,4,10,6,12,6,3,14,16,12,18,10,6,10,22,18,20,12,24,14,
%T 28,2,30,30,9,16,5,30,36,18,12,30,40,6,42,22,30,22,46,42,42,40,15,26,
%U 52,48,10,42,18,28,58,30,60,30,42,62,10,6,66,34,21,4,70,66,72,36,60,38,7,12
%N a(n) = largest integer < n such that the positive integers <= a(n) and coprime to a(n) are also coprime to n.
%e The positive integers k, k <= 6, where the positive integers <= k and coprime to k are also coprime to 6, are 1,2,6. So a(6) = the largest of these < 6, which is 2.
%t f[n_] := Select[Range[n], GCD[ #, n] == 1 &];g[n_] := Select[Range[n - 1], Times @@ GCD[f[ # ], n] == 1 &];Max /@ Table[g[n], {n, 2, 80}] (* Ray Chandler, Dec 24 2006 *)
%Y Cf. A126260, A073353.
%K nonn
%O 2,2
%A _Leroy Quet_, Dec 24 2006
%E Extended by _Ray Chandler_, Dec 24 2006