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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 31 |
| 5 | 227 |
| 6 | 1782 |
| 7 | 15564 |
| 8 | 151455 |
| 9 | 1635703 |
| 10 | 19457998 |
| 11 | 252962528 |
| 12 | 3568119351 |
| 13 | 54262590843 |
| 14 | 884831668974 |
| 15 | 15397747311556 |
| 16 | 284767367151241 |
| 17 | 5576696534340377 |
| 18 | 115269731259650802 |
| 19 | 2507575460681918232 |
| 20 | 57262481202198407625 |
| 21 | 1369461739333488200365 |
[0,0,4,31,227,1782,15564,151455,1635703,19457998, 252962528,3568119351,54262590843,884831668974, 15397747311556,284767367151241,5576696534340377, 115269731259650802,2507575460681918232, 57262481202198407625,1369461739333488200365] |