Question

Let σ(n) denotes the sum of digits of a natural number n. If N is the smallest natural number such that σ(N) = 2020, then find the value of σ(5N + 2021).

Answer 1

Answer:

n+2n+3n+......+99n

n(1+2+3+..........+99)

n

2

(99)(100)

=9×25×22×n is a perfect square when n=22

Number of digits in n=3

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