I had too much time on my hands and thought this one up.
The answer is 1420.
Looking at the 11th-20th primes, we do the following:
Multiply the prime by the nth spot it holds,
average the next two primes, and repeat.
31x11 (341), average 37 & 41 (39), 43x14 (602), average 47 & 53 (50), 59x17 (1003), average 61 & 67 (64), 71x20 (1420).
This is an original problem.
Comments: (
You must be logged in to post comments.)