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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 76 |
| 5 | 300 |
| 6 | 1240 |
| 7 | 5248 |
| 8 | 22756 |
| 9 | 100284 |
| 10 | 448560 |
| 11 | 2029136 |
| 12 | 9270932 |
| 13 | 42703340 |
| 14 | 198101040 |
| 15 | 924561552 |
| 16 | 4338029924 |
| 17 | 20448459100 |
| 18 | 96785899376 |
| 19 | 459773170064 |
| 20 | 2191233247220 |
| 21 | 10473712211788 |
| 22 | 50194430713392 |
| 23 | 241126154392912 |
| 24 | 1160840600662980 |
| 25 | 5599601532727100 |
| 26 | 27059814204705648 |
| 27 | 130981750805664592 |
[1,2,6,20,76,300,1240,5248,22756,100284,448560, 2029136,9270932,42703340,198101040,924561552, 4338029924,20448459100,96785899376,459773170064, 2191233247220,10473712211788,50194430713392, 241126154392912,1160840600662980,5599601532727100, 27059814204705648,130981750805664592] |