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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 3 |
| 3 | 10 |
| 4 | 45 |
| 5 | 249 |
| 6 | 1709 |
| 7 | 13912 |
| 8 | 131168 |
| 9 | 1402706 |
| 10 | 16757321 |
| 11 | 221018769 |
| 12 | 3188425939 |
| 13 | 49925523804 |
| 14 | 843121969923 |
| 15 | 15272776193787 |
| 16 | 295372123082865 |
| 17 | 6073931908657770 |
| 18 | 132329525329523223 |
| 19 | 3044691799670213778 |
| 20 | 73771773281455834427 |
| 21 | 1877511491197391256001 |
[1,1,3,10,45,249,1709,13912,131168,1402706, 16757321,221018769,3188425939,49925523804, 843121969923,15272776193787,295372123082865, 6073931908657770,132329525329523223, 3044691799670213778,73771773281455834427, 1877511491197391256001] |