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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 104 |
| 5 | 661 |
| 6 | 4812 |
| 7 | 39607 |
| 8 | 364240 |
| 9 | 3704617 |
| 10 | 41310740 |
| 11 | 501328411 |
| 12 | 6578864184 |
| 13 | 92843236669 |
| 14 | 1402257345244 |
| 15 | 22570640656831 |
| 16 | 385718738160032 |
| 17 | 6975222838783057 |
| 18 | 133078088319220260 |
| 19 | 2671441145266564387 |
| 20 | 56287972249358876680 |
| 21 | 1242089553461115778021 |
[0,1,4,19,104,661,4812,39607,364240,3704617, 41310740,501328411,6578864184,92843236669, 1402257345244,22570640656831,385718738160032, 6975222838783057,133078088319220260, 2671441145266564387,56287972249358876680, 1242089553461115778021] |