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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 15 |
| 3 | 57 |
| 4 | 220 |
| 5 | 858 |
| 6 | 3368 |
| 7 | 13276 |
| 8 | 52479 |
| 9 | 207861 |
| 10 | 824527 |
| 11 | 3274395 |
| 12 | 13015081 |
| 13 | 51769813 |
| 14 | 206045841 |
| 15 | 820475513 |
| 16 | 3268499356 |
| 17 | 13025237058 |
| 18 | 51922543076 |
| 19 | 207034128448 |
| 20 | 825713206746 |
| 21 | 3293865399518 |
| 22 | 13142007903586 |
| 23 | 52443095356218 |
| 24 | 209304385553096 |
| 25 | 835459642193284 |
[1,4,15,57,220,858,3368,13276,52479,207861,824527, 3274395,13015081,51769813,206045841,820475513, 3268499356,13025237058,51922543076,207034128448, 825713206746,3293865399518,13142007903586, 52443095356218,209304385553096,835459642193284] |