n | a(n) |
---|---|
0 | 0 |
1 | 1 |
2 | 4 |
3 | 18 |
4 | 88 |
5 | 470 |
6 | 2724 |
7 | 17010 |
8 | 113712 |
9 | 809262 |
10 | 6101820 |
11 | 48540778 |
12 | 405935688 |
13 | 3557404838 |
14 | 32577733972 |
15 | 310987560930 |
16 | 3087723669600 |
17 | 31823217868318 |
18 | 339845199259500 |
19 | 3754422961010522 |
20 | 42843681016834680 |
21 | 504339820818380694 |
[0,1,4,18,88,470,2724,17010,113712,809262,6101820, 48540778,405935688,3557404838,32577733972, 310987560930,3087723669600,31823217868318, 339845199259500,3754422961010522, 42843681016834680,504339820818380694] |