The sum of the digits of a number formed by any power or index of 9 is always 9.

**(v)** 9 x 7 = 63 → 6 + 3 = 9

**(vi)** 9 x 15 = 135 → 1 + 3 + 5 = 9

**(vii)** 9 x 17 = 153 → 1 + 5 + 3 = 9

**(viii)** 9 x 19 = 171 → 1 + 7 + 1 = 9

**Related Concept**

● Patterns and Mental Mathematics

● Counting Numbers in Proper Pattern

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● Patterns

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