ONE SHEEP ON FIFTEEN ON TWENTY

 

Or 36 sheep to you....

Welsh counting is mental

From Wiki:-

The traditional counting system used in the Welsh language is vigesimal, i.e. based on twenties where numbers from 11 to 14 are "1–4 on ten", 16–19 are "1–4 on fifteen" (though 18 is more commonly "two nines"); numbers from 21 to 39 are "1–19 on twenty", 40 is "two twenty", 60 is "three twenty", etc.

There is also a decimal counting system, where numbers are "x ten y" unit(s), e.g. thirty-five (35) in decimal is tri deg pump (three ten five) while in vigesimal it is pymtheg ar hugain (fifteen – itself "five-ten" – on twenty).

So:-

Number	Vigesimal system	Decimal system
0	sero/dim
1	un
2	dau (m), dwy (f)
3	tri (m), tair (f)
4	pedwar (m), pedair (f)
5	pum(p)
6	chwe(ch)
7	saith
8	wyth
9	naw
10	deg/un deg, deng
11	un ar ddeg ("one on ten")	un deg un
12	deuddeg, deuddeng	un deg dau/dwy
13	tri/tair ar ddeg	un deg tri/tair
14	pedwar/pedair ar ddeg	un deg pedwar/pedair
15	pymtheg, pymtheng	un deg pump
16	un ar bymtheg ("one on fifteen")	un deg chwech
17	dau/dwy ar bymtheg	un deg saith
18	deunaw/tri/tair ar bymtheg ("two nines"/"three on fifteen")	un deg wyth
19	pedwar/pedair ar bymtheg	un deg naw
20	ugain	dau ddeg
21	un ar hugain ("one on twenty")	dau ddeg un
22	dau/dwy ar hugain	dau ddeg dau/dwy
23	tri/tair ar hugain	dau ddeg tri/tair
24	pedwar/pedair ar hugain	dau ddeg pedwar/pedair
25	pump ar hugain	dau ddeg pump
etc.
30	deg ar hugain ("ten on twenty")	tri deg
31	un ar ddeg ar hugain	tri deg un
32	deuddeg ar hugain	tri deg dau/dwy
40	deugain ("two twenty")	pedwar deg
41	deugain ac un ("two twenty and one")	pedwar deg un
50	hannercant/deg a deugain ("half a hundred"/"ten and forty")	pum deg
51	un ar ddeg a deugain	pum deg un hanner cant ac un
60	trigain ("three twenty")	chwe deg
61	trigain ac un	chwe deg un
70	deg a thrigain ("ten and three twenty")	saith deg
71	un ar ddeg a thrigain ("one on ten and three twenty")	saith deg un
80	pedwar ugain ("four twenty")	wyth deg
81	pedwar ugain ac un	wyth deg un
90	deg a phedwar ugain ("ten and four twenty")	naw deg
91	un ar ddeg a phedwar ugain ("one on ten and four twenty")	naw deg un
100	can(t)
200	dau gant
300	tri chant
400	pedwar cant
500	pum cant
600	chwe chant
700	saith cant

Then just to make it a little harder....

There are, for example, masculine and feminine forms of the numbers "two" (dau and dwy), "three" (tri and tair) and "four" (pedwar and pedair), which must agree with the grammatical gender of the objects being counted. The numerals for "five", "six" and "hundred" (pump, chwech and cant) also have reduced forms (pum, chwe, can) when they precede the object they are counting. The words for "ten", "twelve", and "fifteen" (deg, un deg dau/deuddeg, un deg pump/pymtheg) have the alternative forms deng, deuddeng, pymtheng used before nasals (which may be the result of mutation) and, occasionally, vowels;

back in 2009 I explained how to count like a basque miller

Seems they liked 20's too