| n | a(n) |
|---|---|
| 0 | 4 |
| 1 | 15 |
| 2 | 136 |
| 3 | 1470 |
| 4 | 24128 |
| 5 | 478320 |
| 6 | 11464768 |
| 7 | 319326960 |
| 8 | 10178837504 |
| 9 | 364859900160 |
| 10 | 14534008182784 |
| 11 | 636808845089280 |
| 12 | 30439017021980672 |
| 13 | 1576198832606638080 |
| 14 | 87897652978230894592 |
| 15 | 5251777898245369559040 |
| 16 | 334706615832128692944896 |
| 17 | 22664760114438656410583040 |
| 18 | 1625030662504773488747216896 |
| 19 | 122985265288422439779648798720 |
[4,15,136,1470,24128,478320,11464768,319326960, 10178837504,364859900160,14534008182784, 636808845089280,30439017021980672, 1576198832606638080,87897652978230894592, 5251777898245369559040,334706615832128692944896, 22664760114438656410583040, 1625030662504773488747216896, 122985265288422439779648798720] |