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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 21 |
| 3 | 99 |
| 4 | 471 |
| 5 | 1935 |
| 6 | 8031 |
| 7 | 32319 |
| 8 | 130431 |
| 9 | 522495 |
| 10 | 2094591 |
| 11 | 8381439 |
| 12 | 33544191 |
| 13 | 134189055 |
| 14 | 536829951 |
| 15 | 2147368959 |
| 16 | 8589770751 |
| 17 | 34359279615 |
| 18 | 137438298111 |
| 19 | 549753978879 |
| 20 | 2199020634111 |
| 21 | 8796085682175 |
| 22 | 35184361603071 |
| 23 | 140737458995199 |
| 24 | 562949911478271 |
[1,0,21,99,471,1935,8031,32319,130431,522495, 2094591,8381439,33544191,134189055,536829951, 2147368959,8589770751,34359279615,137438298111, 549753978879,2199020634111,8796085682175, 35184361603071,140737458995199,562949911478271] |