The equation transformation of 3a(n+ 1)=3an-2 gives a (n+ 1)-an =-2/3.

So this series is a arithmetic progression with the first term of 15 and the tolerance of -2/3.

The product of two adjacent terms of a series is required to be negative.

We might as well set these two adjacent terms as ap and a(p+ 1).

Know the meaning of the problem: AP * a (p+1) < 0

That is, AP * (AP+d) < 0.

Get 0

AP = A 1+(P- 1) D。

You can get 45/2.

It is a non-zero natural number, so p is 23 and the other term is 24.

Then these two items are 23 and 24.