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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 58 |
| 4 | 208 |
| 5 | 754 |
| 6 | 2770 |
| 7 | 10294 |
| 8 | 38608 |
| 9 | 145858 |
| 10 | 554266 |
| 11 | 2116294 |
| 12 | 8112466 |
| 13 | 31201798 |
| 14 | 120349798 |
| 15 | 465352558 |
| 16 | 1803241168 |
| 17 | 7000818658 |
| 18 | 27225405898 |
| 19 | 106035791398 |
| 20 | 413539586458 |
| 21 | 1614773623318 |
| 22 | 6312296891158 |
| 23 | 24700292182798 |
| 24 | 96742811049298 |
| 25 | 379231819313254 |
[1,4,16,58,208,754,2770,10294,38608,145858,554266, 2116294,8112466,31201798,120349798,465352558, 1803241168,7000818658,27225405898,106035791398, 413539586458,1614773623318,6312296891158, 24700292182798,96742811049298,379231819313254] |