Problem #280
777 Strikes Again
Given N = 777...777 (19 digits) . Find the number of values r\ (0 \leq r \leq N) such that ^{N}C_{r} is divisible by 31 . Since the number of such values can be huge, compute the answer modulo \left(10^9 + 7 \right)
Given N = 777...777 (19 digits) . Find the number of values r\ (0 \leq r \leq N) such that ^{N}C_{r} is divisible by 31 . Since the number of such values can be huge, compute the answer modulo \left(10^9 + 7 \right)