First 20 Fibonacci numbers:
1: 0
2: 1
3: 1
4: 2
5: 3
6: 5
7: 8
8: 13
9: 21
10: 34
11: 55
12: 89
13: 144
14: 233
15: 377
16: 610
17: 987
18: 1597
19: 2584
20: 4181
