The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 18 |
| 4 | 312 |
| 5 | 2340 |
| 6 | 11160 |
| 7 | 39990 |
| 8 | 117648 |
| 9 | 299592 |
| 10 | 683280 |
| 11 | 1428570 |
| 12 | 2783880 |
| 13 | 5118828 |
| 14 | 8964072 |
| 15 | 15059070 |
| 16 | 24408480 |
| 17 | 38347920 |
| 18 | 58619808 |
| 19 | 87460002 |
| 20 | 127695960 |
| 21 | 182857140 |
| 22 | 257298360 |
| 23 | 356336838 |
| 24 | 486403632 |
| 25 | 655210200 |
| 26 | 871930800 |
| 27 | 1147401450 |
[0,0,18,312,2340,11160,39990,117648,299592,683280, 1428570,2783880,5118828,8964072,15059070,24408480, 38347920,58619808,87460002,127695960,182857140, 257298360,356336838,486403632,655210200,871930800, 1147401450] |