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| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 16 |
| 5 | 63 |
| 6 | 239 |
| 7 | 895 |
| 8 | 3343 |
| 9 | 12503 |
| 10 | 46905 |
| 11 | 176620 |
| 12 | 667664 |
| 13 | 2533699 |
| 14 | 9650737 |
| 15 | 36887383 |
| 16 | 141448958 |
| 17 | 544022417 |
| 18 | 2098082719 |
| 19 | 8111788699 |
| 20 | 31434420426 |
| 21 | 122068414186 |
| 22 | 474932563378 |
| 23 | 1851059631879 |
| 24 | 7226108097869 |
| 25 | 28250493771358 |
| 26 | 110594307388370 |
| 27 | 433488248791630 |
[0,0,1,4,16,63,239,895,3343,12503,46905,176620, 667664,2533699,9650737,36887383,141448958, 544022417,2098082719,8111788699,31434420426, 122068414186,474932563378,1851059631879, 7226108097869,28250493771358,110594307388370, 433488248791630] |