A128269 - OEIS

%I #15 Mar 04 2018 17:43:50

%S 1,1,2,2,12,2,60,2,30,2,570,2,4116,2,144,2,39600,2,747694,2,9720308,2,

%T 115638138,2,1261104380,2,3814717230,2,137331022698,2,2137994925180,2,

%U 8901006912,2,274682981784,2,46154014360092,2,29022598622,2

%N a(1)=1; a(n) = lcm((number of earlier terms which are coprime to n), (sum of the earlier terms which are coprime to n)).

%C For n > 2, a(n) is even since by induction the sum of coprimes is 1+1+some even numbers. Therefore a(n) = 2 for even n > 2 since only the 1's are coprime.

%H H. v. Eitzen, <a href="/A128269/b128269.txt">Table of n, a(n) for n = 1..1000</a>

%e Among {a(1),a(2),...a(8)} the terms which are coprime to 9 are a(1)=a(2)=1 and a(3)=a(4)=a(6)=a(8)=2. There are 6 such terms. And the sum of these terms is 10. So a(8) = lcm(6,10) = 30.

%Y Cf. A128268.

%K nonn

%O 1,3

%A _Leroy Quet_, Feb 22 2007

%E More terms copied from b-file by _Hagen von Eitzen_, Jun 24 2009