It is well-known that n = 1 ∑ ∞ n 1 = 1 + 2 1 + 3 1 + 4 1 + . . . diverges. But how about the sum below?
p prime ∑ p 1 = 2 1 + 3 1 + 5 1 + 7 1 + . . .
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Where can I learn about summation like this and more number theory? Is brilliant.org good for number theory or is it not deep enough for these type of questions?
I saw a theorem early in a number theory book that was similar to this but using the inequality e^(x^2 + x) > 1/(1-x) for 0<=x<=1/2, was able to show that the sum of 1/p for all p <=N is greater than ln(ln(N))-π^2/6.
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List the primes in ascending order p 1 , p 2 , p 3 , . . . . Then any integer positive integer N ≥ 2 can certainly be factorised in terms of the first N (at most) primes, and hence n = 1 ∑ N n 1 ≤ j = 1 ∏ N ( 1 − p j 1 ) − 1 and hence ln ( n = 1 ∑ N n 1 ) ≤ j = 1 ∑ N ln ( 1 − p j 1 ) − 1 = − j = 1 ∑ N ln ( 1 − p j 1 ) = j = 1 ∑ N k = 1 ∑ ∞ k p j k 1 = j = 1 ∑ N p j 1 + j = 1 ∑ N k = 2 ∑ ∞ k p j k 1 ≤ j = 1 ∑ N p j 1 + j = 1 ∑ N k = 2 ∑ ∞ p j 2 1 × k 2 k − 2 1 ≤ j = 1 ∑ N p j 1 + n = 1 ∑ ∞ n 2 1 × k = 2 ∑ ∞ 2 k − 1 1 = j = 1 ∑ N p j 1 + 6 1 π 2 Since ∑ n n − 1 diverges, we deduce that ∑ p p − 1 diverges.