The OEIS is supported by the many generous donors to the OEIS Foundation.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 20 |
| 2 | 388 |
| 3 | 7376 |
| 4 | 138340 |
| 5 | 2572880 |
| 6 | 47652240 |
| 7 | 882388800 |
| 8 | 16402291620 |
| 9 | 307411770320 |
| 10 | 5837516987920 |
| 11 | 112918906836800 |
| 12 | 2237687548230160 |
| 13 | 45677390764531520 |
| 14 | 964818477552462400 |
| 15 | 21148251536958233856 |
| 16 | 481370160754727691300 |
| 17 | 11360399185583414128848 |
| 18 | 277079154699775861823376 |
[1,20,388,7376,138340,2572880,47652240,882388800, 16402291620,307411770320,5837516987920, 112918906836800,2237687548230160, 45677390764531520,964818477552462400, 21148251536958233856,481370160754727691300, 11360399185583414128848,277079154699775861823376] |