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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 6 |
| 2 | 33 |
| 3 | 176 |
| 4 | 930 |
| 5 | 4908 |
| 6 | 25954 |
| 7 | 137712 |
| 8 | 733539 |
| 9 | 3922834 |
| 10 | 21060099 |
| 11 | 113481504 |
| 12 | 613619332 |
| 13 | 3328768344 |
| 14 | 18112655748 |
| 15 | 98833261600 |
| 16 | 540705999621 |
| 17 | 2965360687518 |
| 18 | 16299708148901 |
| 19 | 89784615643728 |
| 20 | 495545294427558 |
[1,6,33,176,930,4908,25954,137712,733539,3922834, 21060099,113481504,613619332,3328768344, 18112655748,98833261600,540705999621, 2965360687518,16299708148901,89784615643728, 495545294427558] |