OFFSET
0,3
COMMENTS
Since the geometric mean of the digits of any number is either 0 or between 1 and 9, "the first d digits" is equivalent to the integer part of this value multiplied by 10^(d-1), which leads to the given formula.
Motivated by sequence A257830.
EXAMPLE
For n = 11, a 2-digit number, the geometric mean of the digits is trivially 1, which is 1.000..., and the first two decimal digits are 10, so a(11) = 10. For n=12, geometric mean is sqrt(2) = 1.414..., so a(12) = 14. - N. J. A. Sloane, May 11 2015
PROG
(PARI) a(n)=sqrtn(prod(i=1, #n=digits(n), n[i]), #n)\10^(1-#n)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
M. F. Hasler, May 10 2015
STATUS
approved