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| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 268 |
| 5 | 4185 |
| 6 | 100146 |
| 7 | 2944921 |
| 8 | 110303880 |
| 9 | 4976190225 |
| 10 | 267276082150 |
| 11 | 16769865552561 |
| 12 | 1212712561009500 |
| 13 | 99940859707310089 |
| 14 | 9294528076388524074 |
| 15 | 967395346945752464265 |
| 16 | 111872727929427271336336 |
| 17 | 14283181659779238236208801 |
| 18 | 2002001211803983519973104974 |
| 19 | 306524554411560349543442894017 |
| 20 | 51035879163206907059508782146980 |
[1,1,4,21,268,4185,100146,2944921,110303880, 4976190225,267276082150,16769865552561, 1212712561009500,99940859707310089, 9294528076388524074,967395346945752464265, 111872727929427271336336, 14283181659779238236208801, 2002001211803983519973104974, 306524554411560349543442894017, 51035879163206907059508782146980] |