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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 0 |
| 2 | 4 |
| 3 | 12 |
| 4 | 56 |
| 5 | 280 |
| 6 | 1488 |
| 7 | 8232 |
| 8 | 47008 |
| 9 | 274824 |
| 10 | 1636520 |
| 11 | 9890584 |
| 12 | 60510480 |
| 13 | 374019776 |
| 14 | 2332131872 |
| 15 | 14651535840 |
| 16 | 92653845120 |
| 17 | 589317728376 |
| 18 | 3767523372432 |
| 19 | 24196006128592 |
| 20 | 156030800105840 |
| 21 | 1009911004804296 |
| 22 | 6558631830442384 |
| 23 | 42723991459518368 |
| 24 | 279091277437885920 |
[1,0,4,12,56,280,1488,8232,47008,274824,1636520, 9890584,60510480,374019776,2332131872,14651535840, 92653845120,589317728376,3767523372432, 24196006128592,156030800105840,1009911004804296, 6558631830442384,42723991459518368, 279091277437885920] |