The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 2 |
| 2 | 2 |
| 3 | 12 |
| 4 | 20 |
| 5 | 72 |
| 6 | 168 |
| 7 | 496 |
| 8 | 1296 |
| 9 | 3616 |
| 10 | 9760 |
| 11 | 26816 |
| 12 | 73024 |
| 13 | 199808 |
| 14 | 545408 |
| 15 | 1490688 |
| 16 | 4071680 |
| 17 | 11125248 |
| 18 | 30392832 |
| 19 | 83037184 |
| 20 | 226857984 |
| 21 | 619792384 |
| 22 | 1693296640 |
| 23 | 4626182144 |
| 24 | 12638949376 |
| 25 | 34530271232 |
| 26 | 94338424832 |
| 27 | 257737408512 |
[2,2,12,20,72,168,496,1296,3616,9760,26816,73024, 199808,545408,1490688,4071680,11125248,30392832, 83037184,226857984,619792384,1693296640, 4626182144,12638949376,34530271232,94338424832, 257737408512] |