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| n | a(n) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 18 |
| 5 | 60 |
| 6 | 186 |
| 7 | 522 |
| 8 | 1380 |
| 9 | 3459 |
| 10 | 8321 |
| 11 | 19332 |
| 12 | 43629 |
| 13 | 96045 |
| 14 | 206953 |
| 15 | 437677 |
| 16 | 910549 |
| 17 | 1866952 |
| 18 | 3778561 |
| 19 | 7558953 |
| 20 | 14963504 |
| 21 | 29340482 |
| 22 | 57033862 |
| 23 | 109989752 |
| 24 | 210575822 |
| 25 | 400452782 |
| 26 | 756836537 |
| 27 | 1422191570 |
| 28 | 2658250044 |
| 29 | 4943946756 |
| 30 | 9152396892 |
[0,1,4,18,60,186,522,1380,3459,8321,19332,43629, 96045,206953,437677,910549,1866952,3778561, 7558953,14963504,29340482,57033862,109989752, 210575822,400452782,756836537,1422191570, 2658250044,4943946756,9152396892] |