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A220712 as a simple table
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 21 |
| 4 | 129 |
| 5 | 932 |
| 6 | 6412 |
| 7 | 44976 |
| 8 | 311193 |
| 9 | 2168111 |
| 10 | 15034974 |
| 11 | 104478616 |
| 12 | 725286308 |
| 13 | 5037269200 |
| 14 | 34977393156 |
| 15 | 242898931716 |
| 16 | 1686719471828 |
| 17 | 11713075485508 |
| 18 | 81338093590180 |
| 19 | 564832581201972 |
| 20 | 3922330554994484 |
| 21 | 27237632538545092 |
[1,1,21,129,932,6412,44976,311193,2168111, 15034974,104478616,725286308,5037269200, 34977393156,242898931716,1686719471828, 11713075485508,81338093590180,564832581201972, 3922330554994484,27237632538545092] |