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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 3 |
| 2 | 31 |
| 3 | 248 |
| 4 | 1941 |
| 5 | 15334 |
| 6 | 122915 |
| 7 | 999456 |
| 8 | 8231740 |
| 9 | 68562887 |
| 10 | 576661761 |
| 11 | 4891506968 |
| 12 | 41801697070 |
| 13 | 359574305580 |
| 14 | 3111012673755 |
| 15 | 27055673506128 |
| 16 | 236387476114548 |
| 17 | 2073957836402524 |
| 18 | 18264689865840284 |
| 19 | 161403223665821280 |
| 20 | 1430768729986730685 |
| 21 | 12719497076318052990 |
[0,3,31,248,1941,15334,122915,999456,8231740, 68562887,576661761,4891506968,41801697070, 359574305580,3111012673755,27055673506128, 236387476114548,2073957836402524, 18264689865840284,161403223665821280, 1430768729986730685,12719497076318052990] |