This is an easy problem i guess..but don't know why I haven't made much headway in it. Would appreciate a clear solution t this :).
Find the number of natural numbers strictly not greater than 10000 such that 2^n-n^2 is divisible by 7.
I analyzed using mod upto 20 and found 5 cases positive but after that I found there was no consistent pattern and left it.
I would kindly request one and all to come forward and solve this. Thanks