When a= 1, b can take 1, with five * * *.

When a=2, b can take 1, 3,5 * * * and there are two (the rest are repeated).

When a=3, b can take 1, 2, 4, 5 * * and there are four (the rest are repeated).

When a=4, b can take 1, 2, 3, 5*** and there are four (the rest are repeated).

When a=5, b can be 1, 2, 3, 4, 6 * * and there are five (when 5 is taken, the result is 1, repeated).

When a=6, b can be 1, 2, 3, 4, 5 * * and there are five (when 6 is taken, the result is 1, which is repeated).

So the number of elements is

5+2+4+4+5+5=25 (piece)