| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 20 |
| 3 | 161 |
| 4 | 900 |
| 5 | 4225 |
| 6 | 18196 |
| 7 | 75185 |
| 8 | 304836 |
| 9 | 1225905 |
| 10 | 4913620 |
| 11 | 19669121 |
| 12 | 78697220 |
| 13 | 314817441 |
| 14 | 1259308180 |
| 15 | 5037283345 |
| 16 | 20149198916 |
| 17 | 80596879185 |
| 18 | 322387621716 |
| 19 | 1289550617185 |
| 20 | 5158202628740 |
| 21 | 20632810709441 |
[1,20,161,900,4225,18196,75185,304836,1225905, 4913620,19669121,78697220,314817441,1259308180, 5037283345,20149198916,80596879185,322387621716, 1289550617185,5158202628740,20632810709441] |