n | a(n) |
---|---|
0 | 1 |
1 | 4 |
2 | 20 |
3 | 116 |
4 | 740 |
5 | 5028 |
6 | 35700 |
7 | 261780 |
8 | 1967300 |
9 | 15072836 |
10 | 117297620 |
11 | 924612532 |
12 | 7367204260 |
13 | 59240277988 |
14 | 480118631220 |
15 | 3917880562644 |
16 | 32163325863300 |
17 | 265446382860420 |
18 | 2201136740855700 |
19 | 18329850024033012 |
20 | 153225552507991140 |
[1,4,20,116,740,5028,35700,261780,1967300, 15072836,117297620,924612532,7367204260, 59240277988,480118631220,3917880562644, 32163325863300,265446382860420,2201136740855700, 18329850024033012,153225552507991140] |