please answer it quickly
Kindly refer the similar link for your query.
https://www.meritnation.com/ask-answer/question/let-an-denote-the-number-of-all-n-digit-positive-integers-fo/permutations-and-combinations/8504479
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https://www.meritnation.com/ask-answer/question/let-an-denote-the-number-of-all-n-digit-positive-integers-fo/permutations-and-combinations/8504479
Regards