I was waiting for someone to say "the number one." It's tricky. I once told a guy I'd give him a dollar if he disproved the Law of Fives, and every day he could make one attempt to stump me, and I'd have until the next day to solve it. After several weeks, he gave me the number one. And the next day I said to him, "one is the number of dollars you'd get if you disproved the Law of Fives." He gave up after that. <:]
Other than that, one person has five extremities (arms, legs, head). And one hand has five fingers. One brain commands five senses. Five elements make up one universe. Earth, air, fire, water, and ether; Five become one. And one is five.