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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 15 |
| 3 | 169 |
| 4 | 1695 |
| 5 | 15961 |
| 6 | 26846 |
| 7 | 450066 |
| 8 | 5247614 |
| 9 | 13156907 |
| 10 | 226316077 |
| 11 | 680627620 |
| 12 | 13354327932 |
| 13 | 65310761853 |
| 14 | 328708074010 |
| 15 | 1951441519231 |
| 16 | 15611532153848 |
| 17 | 158125187800385 |
| 18 | 101848932467045 |
| 19 | 7328445851378156 |
| 20 | 35829776440278962 |
| 21 | 286638211522231696 |
[0,1,15,169,1695,15961,26846,450066,5247614, 13156907,226316077,680627620,13354327932, 65310761853,328708074010,1951441519231, 15611532153848,158125187800385,101848932467045, 7328445851378156,35829776440278962, 286638211522231696] |