In seventh grade, the harder the math problem, the better. What do the answers and problem-solving skills before the linear equation of one variable (including linear equation of one variable) explain? ... 1. Write down the natural number 1, 2, 3, 4, 5 ... and form one number at a time:12345678910112. ...

2. In the book 1, 2, 3, ..., 1995, find all positive integers satisfying the following conditions.

A: (1995+a)| 1995a

Supplementary question: "|" means that the latter is divisible by the former.

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1 is divisible by 72, that is, by 8 and 9.

Conditions that can be divisible by 8: the last three digits can be divisible by 8;

Conditions that can be divisible by 9: The number obtained by adding the digits of this number can be divisible by 9.

A number divided by 9 is equal to the sum of digits divided by 9.

This number is123456789112131415 ... 31323 3343533.

That is, write to 36.

2. let 1995a/( 1995+a)=b,

Factorization results in (1995+a) (1995-b) =19952.

And19952 = 32 * 52 * 72 *192.

If we make a < 1995, that is, 1995 2 is decomposed into two numbers, one of which is greater than 1995 and less than 1995+ 1995=3990.

There are several factors that can meet this requirement:

1995^2=2527* 1575

=3249* 1225

=3675* 1083

=2205* 1805

=2793* 1425

=3325* 1 197

At this time, the values of a are: 532, 1254, 1680, 2 10/0,798, 1330 respectively.