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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 7 |
| 3 | 40 |
| 4 | 217 |
| 5 | 1156 |
| 6 | 6097 |
| 7 | 31900 |
| 8 | 165697 |
| 9 | 855076 |
| 10 | 4387537 |
| 11 | 22404460 |
| 12 | 113945377 |
| 13 | 577590196 |
| 14 | 2919923377 |
| 15 | 14729076220 |
| 16 | 74167952257 |
| 17 | 372944296516 |
| 18 | 1873182473617 |
| 19 | 9399885079180 |
| 20 | 47135702874337 |
| 21 | 236224784974036 |
[0,1,7,40,217,1156,6097,31900,165697,855076, 4387537,22404460,113945377,577590196,2919923377, 14729076220,74167952257,372944296516, 1873182473617,9399885079180,47135702874337, 236224784974036] |