Question

Find the next number in the series 0, 0, 3, 20, 115

I've spent about 30 minutes on it but can't get it.

Answer 1

Here's a clue:

1-1 = 0
2-2 = 0
6-3 = 3
24-4 = 20

Answer 2

AH! Very good!
Factorials! 1! - 1 = 0
2! -2 = 0 etc

Answer 3

what might have made that more difficult is if they had included 0! which is 0! - 0 = 1

1 , 0, 0, 3, 20 would seem very odd!

Answer 4

bingo. there's an online dictionary of integer sequences, btw. https://oeis.org/A005096

Answer 5

ok thanx

Answer 6

if ever you are having trouble with insomnia, reading a few pages of it ought to do the trick :-)

Answer 7

lol! yeah!