Divisibility streaks (noch nicht übersetzt)
Problem 601
For every positive number n we define the function streak(n)=k as the smallest positive integer k such that n+k is not divisible by k+1.
E.g:
13 is divisible by 1
14 is divisible by 2
15 is divisible by 3
16 is divisible by 4
17 is NOT divisible by 5
So streak(13)=4.
Similarly:
120 is divisible by 1
121 is NOT divisible by 2
So streak(120)=1.
Define P(s,N) to be the number of integers n, 1<n<N, for which streak(n)=s.
So P(3,14)=1 and P(6,106)=14286.
Find the sum, as i ranges from 1 to 31, of P(i,4i).