A124443 - OEIS

%I #12 Mar 18 2018 04:01:31

%S 1,1,1,1,2,1,6,3,4,3,60,5,60,15,28,105,840,35,2520,63,40,315,27720,

%T 385,5544,3465,40040,6435,360360,1001,360360,45045,7280,45045,350064,

%U 85085,12252240,765765,1989680,2909907,232792560,230945,232792560,1322685

%N a(1)=1, a(n) = LCM of the integers, from 1 to n/2, which are coprime to n.

%e The integers which are >= 1 and are <= 9/2 and which are coprime to 9 are 1, 2 and 4. So a(9) = lcm(1,2,4) = 4.

%t f[n_] := If[n == 1, 1, LCM @@ Select[Range[Floor[n/2]], GCD[ #, n] == 1 &]];Table[f[n], {n, 45}] (* _Ray Chandler_, Nov 12 2006 *)

%o (PARI) a(n) = lcm(select(x->(gcd(x, n)==1), vector(n\2, k, k))); \\ _Michel Marcus_, Mar 18 2018

%Y Cf. A124444.

%K nonn

%O 1,5

%A _Leroy Quet_, Nov 01 2006

%E Extended by _Ray Chandler_, Nov 12 2006