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8 years, 8 months ago
8 years, 8 months ago
The sum of all co-primes below a given number = E(n)*N/2.
Here E(N) is Euler's Totient Function for that number. So total numbers below 100 which are coprime to 2,3 and 5 is given by
100*1*2*4/(2*3*5) = 20*8/6 = 160/6
So sum of all these numbers = 100*160/12 = 1333