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| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 10 |
| 5 | 40 |
| 6 | 250 |
| 7 | 2560 |
| 8 | 32590 |
| 9 | 543100 |
| 10 | 10242790 |
| 11 | 233335660 |
| 12 | 6703028890 |
| 13 | 207263519020 |
| 14 | 7628001653830 |
| 15 | 311878265181040 |
| 16 | 13394639596851070 |
| 17 | 628284422185342480 |
| 18 | 33217442899375387210 |
| 19 | 1955977793053588026280 |
[1,2,4,10,40,250,2560,32590,543100,10242790, 233335660,6703028890,207263519020,7628001653830, 311878265181040,13394639596851070, 628284422185342480,33217442899375387210, 1955977793053588026280] |