Number Theory Functions

[avkalb <avkalb panix com>]

Using Gnumeric Spreadsheet 1.10.1 and 64-bit Sidux.

The Gnumeric Manual, Version 1.10, section A13 indicates some number theory
calculations are available.  I have briefly examined a few:

Some functions give me reasonable outputs for simple test inputs:
   Isprime, ithprime, nt_pi,  nt_sigma, and pfactor.

But nt_d doesn't  seem to work as I expected.  nt_d(n) is supposed to 
calculate the number of divisors of n
according to function reference A13 in The Gnumeric Manual, Version 1.10

If you select the insert function from the menu bar and then select nt_d 
from the listing,  an example is given
that nt_d(4096) = 13. In actuality, 2^12 = 4096 i.e there are 12 
divisors of 2 in 4096.  If 1 also is included
as a divisor then 13 would be correct.

But that doesn't explain the following results:

nt_d(15) =  4 
nt_d(21) =  4
nt_d(70) =  8

though it would explain these:
n             7    11    31    16
nt_d(n)    2     2      2      5

What's wrong?  Am I misinterpreting what the function is supposed to 
do?  Any suggestions?