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| n | a(n) |
|---|---|
| 1 | 3 |
| 2 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 18 |
| 6 | 58 |
| 7 | 186 |
| 8 | 594 |
| 9 | 1898 |
| 10 | 6390 |
| 11 | 21402 |
| 12 | 71350 |
| 13 | 237522 |
| 14 | 824130 |
| 15 | 2840594 |
| 16 | 9735090 |
| 17 | 33326370 |
| 18 | 117518870 |
| 19 | 412260450 |
| 20 | 1439364870 |
| 21 | 5017074450 |
| 22 | 17912831754 |
| 23 | 63634522842 |
| 24 | 225032003602 |
| 25 | 794803982874 |
| 26 | 2859133321638 |
| 27 | 10244767026810 |
| 28 | 36572931177942 |
[3,1,2,6,18,58,186,594,1898,6390,21402,71350, 237522,824130,2840594,9735090,33326370,117518870, 412260450,1439364870,5017074450,17912831754, 63634522842,225032003602,794803982874, 2859133321638,10244767026810,36572931177942] |