The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 3 |
| 2 | 15 |
| 3 | 73 |
| 4 | 360 |
| 5 | 1800 |
| 6 | 9112 |
| 7 | 46632 |
| 8 | 240936 |
| 9 | 1255336 |
| 10 | 6589080 |
| 11 | 34811784 |
| 12 | 184990568 |
| 13 | 988156872 |
| 14 | 5303039256 |
| 15 | 28579068520 |
| 16 | 154605138984 |
| 17 | 839272725864 |
| 18 | 4570409517848 |
| 19 | 24961191298248 |
| 20 | 136688674353000 |
| 21 | 750355591919240 |
| 22 | 4128471397725336 |
| 23 | 22762905189252264 |
[1,3,15,73,360,1800,9112,46632,240936,1255336, 6589080,34811784,184990568,988156872,5303039256, 28579068520,154605138984,839272725864, 4570409517848,24961191298248,136688674353000, 750355591919240,4128471397725336, 22762905189252264] |