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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 96 |
| 5 | 265 |
| 6 | 672 |
| 7 | 1617 |
| 8 | 3776 |
| 9 | 8577 |
| 10 | 19080 |
| 11 | 41745 |
| 12 | 90048 |
| 13 | 191945 |
| 14 | 404992 |
| 15 | 846945 |
| 16 | 1757440 |
| 17 | 3621697 |
| 18 | 7417800 |
| 19 | 15109313 |
| 20 | 30623520 |
| 21 | 61788489 |
| 22 | 124158496 |
| 23 | 248549937 |
| 24 | 495852480 |
| 25 | 986076225 |
| 26 | 1955203016 |
| 27 | 3866245425 |
| 28 | 7625813888 |
| 29 | 15005718153 |
[1,4,18,96,265,672,1617,3776,8577,19080,41745, 90048,191945,404992,846945,1757440,3621697, 7417800,15109313,30623520,61788489,124158496, 248549937,495852480,986076225,1955203016, 3866245425,7625813888,15005718153] |