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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 56 |
| 4 | 209 |
| 5 | 779 |
| 6 | 2898 |
| 7 | 10760 |
| 8 | 39882 |
| 9 | 147612 |
| 10 | 545721 |
| 11 | 2015721 |
| 12 | 7440251 |
| 13 | 27448008 |
| 14 | 101217076 |
| 15 | 373128151 |
| 16 | 1375167467 |
| 17 | 5067236766 |
| 18 | 18669118971 |
| 19 | 68774597447 |
| 20 | 253334948791 |
| 21 | 933111590565 |
| 22 | 3436767111783 |
| 23 | 12657552835178 |
| 24 | 46616152422035 |
| 25 | 171677402416052 |
[1,4,15,56,209,779,2898,10760,39882,147612,545721, 2015721,7440251,27448008,101217076,373128151, 1375167467,5067236766,18669118971,68774597447, 253334948791,933111590565,3436767111783, 12657552835178,46616152422035,171677402416052] |