| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 13 |
| 5 | 76 |
| 6 | 421 |
| 7 | 3424 |
| 8 | 26713 |
| 9 | 277456 |
| 10 | 2794441 |
| 11 | 35345344 |
| 12 | 436186213 |
| 13 | 6504742336 |
| 14 | 95033434861 |
| 15 | 1632531979264 |
| 16 | 27555582190513 |
| 17 | 535821754153216 |
| 18 | 10260037095841681 |
| 19 | 222769351470429184 |
| 20 | 4771143086720391613 |
[1,1,1,4,13,76,421,3424,26713,277456,2794441, 35345344,436186213,6504742336,95033434861, 1632531979264,27555582190513,535821754153216, 10260037095841681,222769351470429184, 4771143086720391613] |