45. DIVISIBILITY TESTS - EXAMPLES
 
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Pick-up the techniques

Test Divisibility of the famous number, 1729:
1) by 3
1 + 7 + 2 + 9 >> 19 >> 10>> 1;
Not divisible by 3.

2) by 7 (Subtract 2 times ...)
1729 - 2x9 = 154 >> 154 - 2x4 = 7;
Yes, Divisible by 7.

3) by 11
1 + 2 = 3 & 7 + 9 = 16; Difference is 13;
13 is not a multiple of 11. So not divisible by 11.

4) by 13 (Add 4 times ...)
1729 + 4x9 = 208 >> 208 + 4x8 = 52
>> 52 + 4x2 = 13;
Yes, Divisible by 13.

5) by 17 (Subtract 5 times ...)
1729 - 5x9 = 127 >> 127 - 5x7 = -23;
No, Not divisible by 17.

6) by 19 (Add 2 times ...)
1729 + 2x9 = 190;
Yes, Divisible by 19.

7) by 23 (Add 7 times ...)
1729 + 7x9 = 235 >> 235 + 7x5 = 58;
No, Not divisible by 23.