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A001668 as a simple table

na(n)
01
13
26
312
424
548
690
7174
8336
9648
101218
112328
124416
138388
1415780
1529892
1656268
17106200
18199350
19375504
20704304
211323996
222479692
234654464
248710212
2516328220
2630526374
2757161568
28106794084
29199788408
30372996450
31697217994
321300954248

[1,3,6,12,24,48,90,174,336,648,1218,2328,4416,
 8388,15780,29892,56268,106200,199350,375504,
 704304,1323996,2479692,4654464,8710212,16328220,
 30526374,57161568,106794084,199788408,372996450,
 697217994,1300954248]