A member of an integer sequence defined similarly to the Fibonacci numbers, except that each term equals the sum of the previous three terms in the series. The first few terms are thus 1, 1, 2, 4, 7, 13, 24, 44, and 81. The ratio between successive terms converges to approximately 1.83928675521416113255..., which is a root of the polynomial x3 -x2 -x2 -1.

I don't recall the name of the teenage mathematician who named this sequence, but I never forget reading that he died in a motorcycle accident before celebrating his sixth Tribonacci birthday.