A239208 - OEIS

%I #7 Mar 12 2014 11:21:56

%S 18,135,891,4095,10560,13120,14144,21600,23199,74655,144495,192311,

%T 404415,4197375,4612608,5675775,6664680,9180800,10953215,11110400,

%U 14381055,18162144,18420480,18920000,20765024,25159680,32058351,41055200,55889920,65327104,65982464

%N Numbers n such that sigma(n) divides the sum of the numbers x not coprime to n, with x<=n.

%C Numbers n such that sigma(n) | n/2(n+1-phi(n)).

%H Giovanni Resta, <a href="/A239208/b239208.txt">Table of n, a(n) for n = 1..100</a>

%e 18/2*(19-phi(18)) = 117, sigma(18) = 39 and 117 / 39 = 3.

%p with(numtheory); P:=proc(q) local a,n;

%p for n from 1 to q do a:=n/2*(n+1-phi(n)); if type(a/sigma(n),integer) then print(n);

%p fi; od; end: P(10^6);

%Y Cf. A000010, A000230, A238232, A239205.

%K nonn,easy

%O 1,1

%A _Paolo P. Lava_, Mar 12 2014

%E a(14)-a(31) from _Giovanni Resta_, Mar 12 2014