Question 16

A year is called a prime year if that year number is a prime number. For example, 2017 is a prime year. Assume that a person born in 2017 graduates, turns 21 years in the same year. What is the sum of all the prime years starting from the year of his birth to the year of his graduation?


Correct Answer: 6073

Solution

He turns 21 in $$2017 + 21 = 2038$$, so we need the primes from 2017 to 2038. Checking the odd years, $$2019 = 3 \times 673$$, $$2021 = 43 \times 47$$, $$2023 = 7 \times 17^2$$, $$2025 = 45^2$$, $$2031 = 3 \times 677$$, $$2033 = 19 \times 107$$, $$2035 = 5 \times 407$$ and $$2037 = 3 \times 679$$ are composite, while 2017, 2027 and 2029 are prime. The sum is $$2017 + 2027 + 2029 = 6073$$.

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