Hi,
There is a way to check the divisibility by 7.
Check the below:
Divisibility by 7, 11, and 13
Let a number be ....kjihgfedcba where a, b, c, d, are respectively units digits, tens digits, hundreds digits, thousands digits and so on. Starting from right to left, we make groups of three digit numbers successively and continue till the end. It is not necessary that the leftmost group has three digits.
Grouping of the above number in groups of three, from right to left, is done in the following manner kj,ihg,fed,cba
We add the alternate groups (1 st , 3 rd , 5th etc.. and 2nd , 4th , 6th , etc..) to obtain two sets of numbers, N 1 and N 2 .
In the above example, N 1 = cba + ihg and N 2 = fed + kj
Let D be difference of two numbers, N 1 and N 2 i.e. D = N 1 - N 2 .
- If D is divisible by 7, then the original number is divisible by 7.
- If D is divisible by 11, then the original number is divisible by 11
- If D is divisible by 13 then the original number is divisible by 13.
Regards,
Jack