The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 84 |
| 5 | 387 |
| 6 | 1784 |
| 7 | 8228 |
| 8 | 37944 |
| 9 | 174981 |
| 10 | 806940 |
| 11 | 3721270 |
| 12 | 17160940 |
| 13 | 79139079 |
| 14 | 364956336 |
| 15 | 1683025992 |
| 16 | 7761412016 |
| 17 | 35792386313 |
| 18 | 165059516916 |
| 19 | 761185462362 |
| 20 | 3510269016516 |
| 21 | 16187892672139 |
| 22 | 74651791054120 |
| 23 | 344262840164460 |
| 24 | 1587596244438120 |
[0,1,4,18,84,387,1784,8228,37944,174981,806940, 3721270,17160940,79139079,364956336,1683025992, 7761412016,35792386313,165059516916,761185462362, 3510269016516,16187892672139,74651791054120, 344262840164460,1587596244438120] |