# Math Help - number theory

1. ## number theory

in base 5 devise test for:

divisibility by 2,4,5

2. Hello, teeplkyl!

In base-5, devise tests for divisibility by 2, 4, 5

Divisible by 2

If there is an even number of odd digits, the number is divisible by 2.

Examples: . $2143_5$ is even (298). . $4032_5$ is odd (517)

Divisible by 4

If the sum is divisible by 4, the number is divisible by 4.

Example: . $12,032_5\quad\Rightarrow\quad 1+2+0+3+2 \:=\:8$
. . . . . . . .Since 8 is divisible by 4, $12,032_5$ is divisible by 4 (872).

Divisible by 5

A number is divisible by 5 if it ends in zero (0).

3. ## Study Number Theory

It is very difficult to study Number Theory topic. Not many good reference textbooks to study Number Theory.

I use A Friendly Introduction to Number Theory, 3rd Edition to study. This is good reference textbook.

Do you have any other good Number Theory related textbooks recommend?

Regards,

Andy