A207428 - OEIS

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A207428 as a simple table

n	a(n)
1	9
2	81
3	351
4	1521
5	8463
6	47089
7	241087
8	1234321
9	6520459
10	34445161
11	179832029
12	938870881
13	4924284469
14	25827382681
15	135217499129
16	707921987161
17	3708936179293
18	19431812871409
19	101777874172609
20	533081279633809

[9,81,351,1521,8463,47089,241087,1234321,6520459, 34445161,179832029,938870881,4924284469, 25827382681,135217499129,707921987161, 3708936179293,19431812871409,101777874172609, 533081279633809]