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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 6 |
| 4 | 25 |
| 5 | 128 |
| 6 | 754 |
| 7 | 5001 |
| 8 | 37048 |
| 9 | 303930 |
| 10 | 2732395 |
| 11 | 26657106 |
| 12 | 280039786 |
| 13 | 3149224991 |
| 14 | 37729906686 |
| 15 | 479570263690 |
| 16 | 6442902231289 |
| 17 | 91186621152460 |
| 18 | 1355582225366134 |
| 19 | 21112253012491481 |
| 20 | 343672026658191836 |
| 21 | 5834977672879651390 |
| 22 | 103130592695715620419 |
[1,1,2,6,25,128,754,5001,37048,303930,2732395, 26657106,280039786,3149224991,37729906686, 479570263690,6442902231289,91186621152460, 1355582225366134,21112253012491481, 343672026658191836,5834977672879651390, 103130592695715620419] |