A337524 - OEIS

%I #11 Nov 03 2022 15:55:14

%S 0,2,2,6,2,12,2,12,6,12,2,30,2,12,12,20,2,30,2,30,12,12,2,56,6,12,12,

%T 30,2,56,2,30,12,12,12,72,2,12,12,56,2,56,2,30,30,12,2,90,6,30,12,30,

%U 2,56,12,56,12,12,2,132,2,12,30,42,12,56,2,30,12,56,2,132,2,12,30,30

%N a(n) = d(n) * (d(n) - 1), where d is the number of divisors of n (A000005).

%C Number of distinct nonsquare m X n matrices such that m and n are divisors of n.

%H Harvey P. Dale, <a href="/A337524/b337524.txt">Table of n, a(n) for n = 1..1000</a>

%t Table[DivisorSigma[0, n]^2 - DivisorSigma[0, n], {n, 100}]

%t #(#-1)&/@DivisorSigma[0,Range[100]] (* _Harvey P. Dale_, Nov 03 2022 *)

%Y Cf. A000005 (tau).

%Y Equals twice A066446.

%K nonn,easy

%O 1,2

%A _Wesley Ivan Hurt_, Aug 30 2020