In a similar vein, it was only today that I discovered that for a number that is biprime, sometimes called semiprime, the average of its sum of divisors and totient is always one more than the number. Again, this was obvious once I looked into it. The reason is that a biprime number
Thursday, 10 October 2019
Totient and Sigma <--> Primes and Biprimes
Though it was obvious when I looked into it, I only recently realised that, for any prime number, the average of its totient and sum of divisors is equal to the number itself. This is because for a prime number , it's only divisors are itself and , thus the sum of divisors is . For the totient, the only number that is coprime with is 1 and thus the totient is . Adding the sum of divisors and the totient together gives and the average is . Thus formally stated:
In a similar vein, it was only today that I discovered that for a number that is biprime, sometimes called semiprime, the average of its sum of divisors and totient is always one more than the number. Again, this was obvious once I looked into it. The reason is that a biprime number has only two factors, let's say and . Thus . The sum of divisors is thus . For the totient, there are multiples of and multiples of that are coprime with . Thus the totient is , remembering that 1 is regarded as being coprime as well. Adding the sum of divisors and the totient together and averaging, we get: This is all very simple stuff but I'd never seen this connection between the totients and sums of divisors of primes and biprimes formally stated before. Thus formally stated:
In a similar vein, it was only today that I discovered that for a number that is biprime, sometimes called semiprime, the average of its sum of divisors and totient is always one more than the number. Again, this was obvious once I looked into it. The reason is that a biprime number
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