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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 4 |
| 5 | 4 |
| 6 | 4 |
| 7 | 20 |
| 8 | 36 |
| 9 | 52 |
| 10 | 132 |
| 11 | 292 |
| 12 | 580 |
| 13 | 1252 |
| 14 | 2628 |
| 15 | 6196 |
| 16 | 13412 |
| 17 | 28884 |
| 18 | 64516 |
| 19 | 147140 |
| 20 | 327684 |
| 21 | 722116 |
| 22 | 1615236 |
| 23 | 3758292 |
| 24 | 8500772 |
| 25 | 19027572 |
| 26 | 43203204 |
| 27 | 100782308 |
| 28 | 230210884 |
| 29 | 522001572 |
| 30 | 1193084612 |
| 31 | 2800307188 |
| 32 | 6441467748 |
| 33 | 14722404372 |
[1,1,4,4,4,4,20,36,52,132,292,580,1252,2628,6196, 13412,28884,64516,147140,327684,722116,1615236, 3758292,8500772,19027572,43203204,100782308, 230210884,522001572,1193084612,2800307188, 6441467748,14722404372] |