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Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

A218920 as a simple table

na(n)
11
21
34
419
573
6412
72660
821449
9184541
101827841
1120043736
12240206213
133119816216

[1,1,4,19,73,412,2660,21449,184541,1827841,
 20043736,240206213,3119816216]