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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 102 |
| 5 | 590 |
| 6 | 3588 |
| 7 | 22617 |
| 8 | 146460 |
| 9 | 968520 |
| 10 | 6513034 |
| 11 | 44403604 |
| 12 | 306209746 |
| 13 | 2132165062 |
| 14 | 14970030506 |
| 15 | 105862919427 |
| 16 | 753344866662 |
| 17 | 5390772814578 |
| 18 | 38765692377100 |
| 19 | 279999861952626 |
| 20 | 2030439981144348 |
| 21 | 14776796428607224 |
| 22 | 107891287190000212 |
| 23 | 790105506941871258 |
[1,1,4,19,102,590,3588,22617,146460,968520, 6513034,44403604,306209746,2132165062,14970030506, 105862919427,753344866662,5390772814578, 38765692377100,279999861952626,2030439981144348, 14776796428607224,107891287190000212, 790105506941871258] |