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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 88 |
| 5 | 563 |
| 6 | 3812 |
| 7 | 26877 |
| 8 | 195349 |
| 9 | 1453763 |
| 10 | 11024089 |
| 11 | 84885641 |
| 12 | 661948987 |
| 13 | 5217188125 |
| 14 | 41493928665 |
| 15 | 332601055544 |
| 16 | 2684193028375 |
| 17 | 21791893755523 |
| 18 | 177856290438261 |
| 19 | 1458434632623471 |
| 20 | 12009839989925178 |
| 21 | 99275036681040765 |
| 22 | 823456735417367135 |
[0,1,3,15,88,563,3812,26877,195349,1453763, 11024089,84885641,661948987,5217188125, 41493928665,332601055544,2684193028375, 21791893755523,177856290438261,1458434632623471, 12009839989925178,99275036681040765, 823456735417367135] |