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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 13 |
| 4 | 48 |
| 5 | 174 |
| 6 | 664 |
| 7 | 2511 |
| 8 | 9704 |
| 9 | 37446 |
| 10 | 146328 |
| 11 | 571254 |
| 12 | 2245680 |
| 13 | 8828364 |
| 14 | 34861968 |
| 15 | 137681413 |
| 16 | 545275968 |
| 17 | 2160151774 |
| 18 | 8574035128 |
| 19 | 34041458854 |
| 20 | 135331020496 |
| 21 | 538160983688 |
| 22 | 2142066529840 |
| 23 | 8528345610682 |
| 24 | 33977249476432 |
| 25 | 135397971935652 |
| 26 | 539825087330960 |
| 27 | 2152684737685952 |
[1,1,4,13,48,174,664,2511,9704,37446,146328, 571254,2245680,8828364,34861968,137681413, 545275968,2160151774,8574035128,34041458854, 135331020496,538160983688,2142066529840, 8528345610682,33977249476432,135397971935652, 539825087330960,2152684737685952] |