A155220 - OEIS

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A155220 as a simple table

n	a(n)
2	1
3	4
4	10
5	19
6	109
7	692
8	3521
9	31519
10	398368
11	5171923
12	89984622
13	2185316954
14	63742209751
15	2336382318172
16	113584162550499
17	6998045379053544
18	543364715394976386
19	54434393498867053000
20	6983398903852168886345

[1,4,10,19,109,692,3521,31519,398368,5171923, 89984622,2185316954,63742209751,2336382318172, 113584162550499,6998045379053544, 543364715394976386,54434393498867053000, 6983398903852168886345]