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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 58 |
| 4 | 204 |
| 5 | 698 |
| 6 | 2346 |
| 7 | 7774 |
| 8 | 25480 |
| 9 | 82774 |
| 10 | 266946 |
| 11 | 855674 |
| 12 | 2728702 |
| 13 | 8663402 |
| 14 | 27400862 |
| 15 | 86376186 |
| 16 | 271488444 |
| 17 | 851099874 |
| 18 | 2661967502 |
| 19 | 8308462182 |
| 20 | 25883429326 |
| 21 | 80497346294 |
| 22 | 249956869434 |
| 23 | 775048966478 |
| 24 | 2400067860090 |
[1,4,16,58,204,698,2346,7774,25480,82774,266946, 855674,2728702,8663402,27400862,86376186, 271488444,851099874,2661967502,8308462182, 25883429326,80497346294,249956869434,775048966478, 2400067860090] |