A129294 - OEIS

%I #12 Sep 27 2018 13:25:02

%S 1,2,2,3,2,4,2,5,3,5,2,7,2,4,7,5,3,6,2,6,6,6,2,13,4,4,4,8,4,10,3,6,5,

%T 6,5,14,2,6,5,8,3,10,3,8,10,5,3,16,3,9,5,9,2,11,5,8,7,4,3,20,2,5,9,11,

%U 4,18,4,6,5,8,3,14,5,4,8,6,4,17,2,21,5,6,3,16,6,10,8,8,2,14,5,9,7,6,5,16

%N Number of divisors of n^3 - 1 that are not greater than n.

%C a(n) = #{d: d<=n and A068601(n) mod d = 0};

%C a(n)>1 for n>2, see A129295 for m such that a(m)=2: a(A129295(n))=2.

%H R. Zumkeller, <a href="/A129294/b129294.txt">Table of n, a(n) for n = 2..1000</a>

%e a(100) = #{1,3,7,9,11,13,21,27,33,37,39,63,77,91,99} = 15.

%t Table[Count[Divisors[n^3-1],_?(#<n+1&)],{n,2,100}] (* _Harvey P. Dale_, Sep 27 2018 *)

%o (PARI) a(n) = sumdiv(n^3-1, d, d <= n); \\ _Michel Marcus_, Aug 01 2018

%Y Cf. A129292, A129296.

%K nonn

%O 2,2

%A _Reinhard Zumkeller_, Apr 09 2007

%E a(1)=1 removed by _Michel Marcus_, Aug 01 2018