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A025227 as a simple table

na(n)
00
11
22
34
412
540
6144
7544
82128
98544
1035008
11145792
12615296
132625792
1411311616
1549124352
16214838528
17945350144
184182412288
1918593224704
2083015133184
21372090122240
221673660915712
237552262979584
2434178799378432
25155096251351040
26705533929816064

[0,1,2,4,12,40,144,544,2128,8544,35008,145792,
 615296,2625792,11311616,49124352,214838528,
 945350144,4182412288,18593224704,83015133184,
 372090122240,1673660915712,7552262979584,
 34178799378432,155096251351040,705533929816064]