OFFSET
0,2
COMMENTS
Also the smallest factorial having at least n trailing zeros. - Jud McCranie, Oct 05 2010
a(n) ~ 4n, a(n) > 4n. Every positive multiple of 5 occurs as much as the exponent of 5 in the prime factorization. - David A. Corneth, Jul 12 2016
Least k such that A027868(k) >= n. - Robert Israel, Jul 12 2016
REFERENCES
H. Ibstedt, Smarandache Primitive Numbers, Smarandache Notions Journal, Vol. 8, No. 1-2-3, 1997, 216-229.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..1000
FORMULA
MAPLE
1, seq(t $ padic:-ordp(t, 5), t=5..1000, 5); # Robert Israel, Jul 12 2016
MATHEMATICA
lpi[n_]:=Module[{k=1, n5=5^n}, While[!Divisible[k!, n5], k++]; k]; Array[ lpi, 60, 0] (* Harvey P. Dale, Jun 19 2012 *)
PROG
(PARI) a(n) = {k = 1; while (valuation(k!, 5) < n, k++); k; } \\ Michel Marcus, Aug 19 2013
(PARI) a(n) = {my(ck = 4 * n, k = 5 * floor(ck/5), t = 0); if(ck > 0, t = sum(i = 1, logint(ck, 5), ck\=5)); while(t < n, k+=5; t+=valuation(k, 5)); max(1, k)} \\ David A. Corneth, Jul 12 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
Bruce Dearden and Jerry Metzger
STATUS
approved