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A020115 as a simple table
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 5 |
| 4 | 19 |
| 5 | 90 |
| 6 | 524 |
| 7 | 3599 |
| 8 | 28342 |
| 9 | 251532 |
| 10 | 2483878 |
| 11 | 27012164 |
| 12 | 320769441 |
| 13 | 4129906549 |
| 14 | 57302453361 |
| 15 | 852373993745 |
| 16 | 13531437150693 |
| 17 | 228343001917932 |
| 18 | 4081631159283028 |
| 19 | 77040788131467136 |
| 20 | 1531185664112909315 |
[1,1,2,5,19,90,524,3599,28342,251532,2483878, 27012164,320769441,4129906549,57302453361, 852373993745,13531437150693,228343001917932, 4081631159283028,77040788131467136, 1531185664112909315] |