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A000898 as a simple table

na(n)
01
12
26
320
476
5312
61384
76512
832400
9168992
10921184
115222208
1230710464
13186753920
141171979904
157573069568
1650305536256
17342949298688
182396286830080
1917138748412928
20125336396368896
21936222729254912
227136574106003456
2355466948299223040
24439216305474605056
253540846129311916032

[1,2,6,20,76,312,1384,6512,32400,168992,921184,
 5222208,30710464,186753920,1171979904,7573069568,
 50305536256,342949298688,2396286830080,
 17138748412928,125336396368896,936222729254912,
 7136574106003456,55466948299223040,
 439216305474605056,3540846129311916032]