lcm(1, 79) + lcm(2, 79) + lcm(3, 79) + ... + lcm(79, 79) = ?
Note: Here lcm means the least common multiple
79 is prime and therefore relatively prime to each of the numbers with which it's paired, except itself, so other than the last term, the lcm function could be replaced by merely the product. The last term is just 79. Then 79 can be factored out:
79 * ((Sigma{n=1,78}(n)) + 1)
= 79 * (78 * 79 / 2 + 1)
= 243,478
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Posted by Charlie
on 2019-05-08 10:53:48 |
solution
