A005618 - OEIS

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A005618 as a simple table

n	a(n)
0	4
1	16
2	88
3	520
4	3112
5	18664
6	111976
7	671848
8	4031080
9	24186472
10	145118824
11	870712936
12	5224277608
13	31345665640
14	188073993832
15	1128443962984
16	6770663777896
17	40623982667368
18	243743896004200
19	1462463376025192

[4,16,88,520,3112,18664,111976,671848,4031080, 24186472,145118824,870712936,5224277608, 31345665640,188073993832,1128443962984, 6770663777896,40623982667368,243743896004200, 1462463376025192]