| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 124 |
| 5 | 782 |
| 6 | 5144 |
| 7 | 34845 |
| 8 | 241196 |
| 9 | 1697498 |
| 10 | 12104872 |
| 11 | 87246770 |
| 12 | 634425752 |
| 13 | 4647805372 |
| 14 | 34267130928 |
| 15 | 254035385949 |
| 16 | 1892315106252 |
| 17 | 14155536314786 |
| 18 | 106288436980488 |
| 19 | 800753707211430 |
| 20 | 6050872882024520 |
[0,1,4,21,124,782,5144,34845,241196,1697498, 12104872,87246770,634425752,4647805372, 34267130928,254035385949,1892315106252, 14155536314786,106288436980488,800753707211430, 6050872882024520] |