A335708 - OEIS

%I #16 Sep 08 2022 08:46:25

%S 1,2,2,3,2,4,2,4,3,4,6,6,6,4,8,4,8,9,8,8,6,10,6,8,12,6,8,12,10,5,12,

%T 12,9,8,12,8,4,10,8,6,16,12,12,4,8,12,15,12,8,6,12,10,6,18,8,14,8,12,

%U 12,4,12,6,4,16,16,12,8,12,9,12,8,12,20,6,4,18,6,16

%N a(n) is the number of divisors of the n-th Niven number.

%F a(n) = A000005(A005349(n)).

%e The first Niven number is 1 and tau(1) = 1, so a(1) = 1.

%e The second Niven number is 2 and tau(2) = 2, so a(2) = 2.

%e The 11th Niven number is 12 and tau(12) = 6, so a(11) = 6.

%t DivisorSigma[0, Select[Range[265], Divisible[#, Plus @@ IntegerDigits[#]] &]] (* _Amiram Eldar_, Aug 04 2020 *)

%o (Magma) niven:=func<n|n mod &+Intseq(n) eq 0 >;[#Divisors(k):k in [1..300]|niven(k)];

%Y Cf. A000005, A005349, A007953.

%K nonn,base

%O 1,2

%A _Marius A. Burtea_, Aug 04 2020