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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 4 |
| 2 | 16 |
| 3 | 66 |
| 4 | 280 |
| 5 | 1216 |
| 6 | 5380 |
| 7 | 24144 |
| 8 | 109504 |
| 9 | 500488 |
| 10 | 2300128 |
| 11 | 10612224 |
| 12 | 49096720 |
| 13 | 227578432 |
| 14 | 1056304384 |
| 15 | 4907373600 |
| 16 | 22813275520 |
| 17 | 106100835328 |
| 18 | 493609021504 |
| 19 | 2296885357824 |
| 20 | 10689540189184 |
| 21 | 49753373831296 |
| 22 | 231588118339072 |
[1,4,16,66,280,1216,5380,24144,109504,500488, 2300128,10612224,49096720,227578432,1056304384, 4907373600,22813275520,106100835328,493609021504, 2296885357824,10689540189184,49753373831296, 231588118339072] |