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A004253 as a simple table
| n | a(n) |
|---|---|
| 1 | 1 |
| 2 | 4 |
| 3 | 19 |
| 4 | 91 |
| 5 | 436 |
| 6 | 2089 |
| 7 | 10009 |
| 8 | 47956 |
| 9 | 229771 |
| 10 | 1100899 |
| 11 | 5274724 |
| 12 | 25272721 |
| 13 | 121088881 |
| 14 | 580171684 |
| 15 | 2779769539 |
| 16 | 13318676011 |
| 17 | 63813610516 |
| 18 | 305749376569 |
| 19 | 1464933272329 |
| 20 | 7018916985076 |
| 21 | 33629651653051 |
| 22 | 161129341280179 |
[1,4,19,91,436,2089,10009,47956,229771,1100899, 5274724,25272721,121088881,580171684,2779769539, 13318676011,63813610516,305749376569, 1464933272329,7018916985076,33629651653051, 161129341280179] |