A090618 Highest power of 9 dividing n!.

0, 0, 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 2, 2, 2, 3, 3, 3, 4, 4, 4, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 7, 7, 7, 7, 7, 8, 8, 8, 9, 9, 9, 9, 9, 9, 10, 10, 10, 11, 11, 11, 11, 11, 11, 13, 13, 13, 13, 13, 13, 14, 14, 14, 15, 15, 15, 15, 15, 15, 16, 16, 16, 17, 17, 17, 17, 17, 17, 18, 18, 18, 20, 20, 20, 20

Offset: 0

Author

Henry Bottomley, Dec 06 2003

Keywords

• nonn

Examples

			a(9)=2 since 9!=362880=9^2*4480.
		

Crossrefs

Cf. A011371, A054861, A090616, A027868, A054896, A090617.

Programs

Mathematica

IntegerExponent[Range[0,90]!,9] (* Harvey P. Dale, Jun 07 2016 *)

Formula

a(n) =A090622(n, 9) =[A054861(n)/2] =[([n/3]+[n/9]+[n/27]+[n/81]+...)/2].