The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 18 |
| 4 | 64 |
| 5 | 214 |
| 6 | 804 |
| 7 | 2830 |
| 8 | 10890 |
| 9 | 39446 |
| 10 | 153802 |
| 11 | 567328 |
| 12 | 2229518 |
| 13 | 8327630 |
| 14 | 32890296 |
| 15 | 123975918 |
| 16 | 491284276 |
| 17 | 1864701156 |
| 18 | 7406431598 |
| 19 | 28264755206 |
| 20 | 112450465794 |
| 21 | 431021149668 |
| 22 | 1716870815076 |
| 23 | 6604493363092 |
| 24 | 26331034550606 |
| 25 | 101596890593664 |
| 26 | 405325077443804 |
| 27 | 1567943204942594 |
[1,2,6,18,64,214,804,2830,10890,39446,153802, 567328,2229518,8327630,32890296,123975918, 491284276,1864701156,7406431598,28264755206, 112450465794,431021149668,1716870815076, 6604493363092,26331034550606,101596890593664, 405325077443804,1567943204942594] |