A137944 - OEIS

%I #10 Aug 31 2019 06:28:34

%S 2,3,4,5,7,8,9,11,13,16,17,19,23,25,27,29,31,32,36,37,41,43,47,49,53,

%T 59,61,64,67,71,73,79,81,83,89,97,100,101,103,107,109,113,120,121,125,

%U 127,128,131,137,139,144,149,151,157,163,167,168,169,173,179,181,191,193

%N Numbers such that the number of composite divisors is a multiple of the number of prime divisors; a(1)=1.

%H R. Zumkeller, <a href="/A137944/b137944.txt">Table of n, a(n) for n = 1..10000</a>

%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/DivisorFunction.html">Divisor Function</a>

%F A055212(a(n)) mod A001221(a(n)) = 0.

%t aQ[n_] := Divisible[DivisorSigma[0, n] - 1,  PrimeNu[n]]; Select[Range[2, 193], aQ] (* _Amiram Eldar_, Aug 31 2019 *)

%Y Cf. A001221, A055212.

%Y Union of A000961 and A137945.

%K nonn

%O 1,1

%A _Reinhard Zumkeller_, Feb 24 2008