A141242 - OEIS

A141242

a(n) is the number of divisors of the n-th positive integer with a prime number of divisors. In other words, a(n) is the number of divisors of A009087(n).

%I #18 Jan 21 2023 03:41:34

%S 2,2,3,2,2,3,2,2,5,2,2,2,3,2,2,2,2,2,2,3,2,2,2,7,2,2,2,2,5,2,2,2,2,2,

%T 2,2,2,3,2,2,2,2,2,2,2,2,2,3,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,

%U 2,2,3,2,2,2,2,2,2,2,2,2,2,2,3,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2

%N a(n) is the number of divisors of the n-th positive integer with a prime number of divisors. In other words, a(n) is the number of divisors of A009087(n).

%C A009087(n) is of the form p^(a(n)-1), where p is some prime.

%H Michael De Vlieger, <a href="/A141242/b141242.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A000005(A009087(n)).

%t DivisorSigma[0, #] &@ Select[Range@ 500, PrimeQ@ DivisorSigma[0, #] &] (* _Michael De Vlieger_, Aug 19 2017 *)

%Y Cf. A000005, A009087, A141241.

%K nonn

%O 1,1

%A _Leroy Quet_, Jun 16 2008

%E Extended by _Ray Chandler_, Jun 25 2009