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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 2 |
| 2 | 6 |
| 3 | 20 |
| 4 | 73 |
| 5 | 282 |
| 6 | 1131 |
| 7 | 4672 |
| 8 | 19724 |
| 9 | 84752 |
| 10 | 369429 |
| 11 | 1629435 |
| 12 | 7259192 |
| 13 | 32615418 |
| 14 | 147619128 |
| 15 | 672411537 |
| 16 | 3080081649 |
| 17 | 14179056899 |
| 18 | 65562383998 |
| 19 | 304359944046 |
| 20 | 1418000511407 |
| 21 | 6627902117686 |
| 22 | 31071410377680 |
| 23 | 146056590528879 |
| 24 | 688272817354702 |
| 25 | 3250831753441245 |
| 26 | 15386777437834858 |
| 27 | 72971502660653682 |
[1,2,6,20,73,282,1131,4672,19724,84752,369429, 1629435,7259192,32615418,147619128,672411537, 3080081649,14179056899,65562383998,304359944046, 1418000511407,6627902117686,31071410377680, 146056590528879,688272817354702,3250831753441245, 15386777437834858,72971502660653682] |