631 is a prime number.
631 is the maximum number of regions into which 35 lines divide a plane.
631 values of n less than or equal to 1000 produce primes for 2n2 + 144251.
631 has a base 2 representation (1001110111) that begins with its base 5 representation
Researchers "estimate that there are 631 Asian elephants living in Taman Negara National Park--a 4,343 square kilometer (1,676 square mile) protected area in the center of Peninsular Malaysia . . . . The team counted elephant dung piles to estimate population size—a scientifically proven technique that produces accurate figures."--Wildlife Conservation Society press release, Jan. 14, 2009.
Source: Prime Curios!