On Mon, 22 Feb 1999 15:01:32 +0100, Christophe Grandsire
<[log in to unmask]> wrote:

>        I think that Tj'a-ts'a~n counting system is one of the strangest=
 feature
>of Tj'a-ts'a~n (at least for Westerners). I don't know if any other =
conlang
>or natlang has a system resembling it, and would be very happy to know =
that.

The closest thing I have is the Zariva system, which uses both 5 and 7.
The numbers 1-7 are:

1: ai
2: ilai ("twice one")
3: ith
4: sai
5: min
6: minda ("one more than 5")
7: thuu

Certain multiples of 5 and 7 have specific names:

10: hi
15: mist
25: ming
125: leeshek
15,625 (125^2): agaalik
1,953,125 (125^3): nuruthkest

49: thuusi

The numbers from 1 to 125 use various combinations of 5 and 7 with the
following affixes: an- (one less), adan- (two less), -ra (one more) -rad
(two more), il- (twice), ith (3) and sai (4).

8: thuura (7+1)
9: anghi (10-1)
10: hi
11: hina (10+1)
12: hinad (10+2)
13: adammist (15-2)
14: ilthu (2*7)
15: mist
16: mistra (15+1)
17: mistrad (15+2)
18: mistith (15+3)
19: mistsai (15+4)
20: mistmin (15+5)
21: ithuu (3*7)
22: ithuura (3*7+1)
23: adamming (25-2)
24: amming (25-1)
25: ming
26: mingna (25+1)
27: mingnad (25+2)
28: saithuu (4*7)
29: saithuura (4*7+1)
30: ilmist (2*15)
31: ilmistra (2*15+1)
32: mingthuu (25+7)
33: mingthuura (25+7+1)
34: amminthuu (5*7-1)
35: minthuu (5*7)
36: minthuura (5*7+1)
37: minthuurad (5*7+2)
38: mingadammist (25+15-2)
39: mingilthuu (25+2*7)
40: mingmist (25+15)
41: mingmistra (25+15+1)
42: mindathuu (6*7)
43: mindathuura (6*7+1)
44: anithmist (3*15-1)
45: ithmist (3*15)
46: ithmistra (3*15+1)
47: adanthuusi (7*7-2)
48: anthuusi (7*7-1)
49: thuusi (7*7)

After 49, multiples of 7 are less frequently used, and it starts to look
more like a base-5 system.