A173292 a(n)! has exactly 10^n trailing zeros (a(n) = -1 if no such number exists).

5, 45, 405, 4005, 40010, 400005, 4000005, 40000010, 400000015, 4000000015, 40000000015, 400000000015, 4000000000010, 40000000000015, 400000000000020, -1, -1, -1, 4000000000000000020, 40000000000000000015, -1

Offset

0,1

Links

Table of n, a(n) for n=0..20.

David S. Hart, James E. Marengo, Darren A. Narayan, and David S. Ross, On the number of trailing zeros in n!, College Math. J., 39(2) (2008) p 139-145.

A. M. Oller-Marcen, A new look at the trailing zeros of n!, arXiv:0906.4868 [math.NT].

A. M. Oller-Marcen, J. Maria Grau, On the Base-b Expansion of the Number of Trailing Zeros of b^k!, J. Int. Seq. 14 (2011) 11.6.8

Crossrefs

Cf. A173558 (at least 10^n trailing zeros).

Sequence in context: A001260 A088505 A067403 * A173558 A022022 A058410

Adjacent sequences: A173289 A173290 A173291 * A173293 A173294 A173295

Keyword

base,sign

Author

José María Grau Ribas, Feb 15 2010, Feb 22 2010

Status

approved