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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 24 |
| 5 | 129 |
| 6 | 759 |
| 7 | 4455 |
| 8 | 26763 |
| 9 | 161898 |
| 10 | 988438 |
| 11 | 6069228 |
| 12 | 37460952 |
| 13 | 232160184 |
| 14 | 1443830084 |
| 15 | 9005809184 |
| 16 | 56316652784 |
| 17 | 352949825249 |
| 18 | 2216334391919 |
| 19 | 13941409199519 |
| 20 | 87830683173419 |
| 21 | 554096566907069 |
| 22 | 3499981913717189 |
| 23 | 22132830286939649 |
[0,1,4,24,129,759,4455,26763,161898,988438, 6069228,37460952,232160184,1443830084,9005809184, 56316652784,352949825249,2216334391919, 13941409199519,87830683173419,554096566907069, 3499981913717189,22132830286939649] |