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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”).

A023988 as a simple table

na(n)
11
22
34
44
54
66
78
86
97
108
1111
1211
1311
1411
1512
1610
1712
1811
1915
2013
2113
2218
2318
2417
2516
2617
2719
2817

[1,2,4,4,4,6,8,6,7,8,11,11,11,11,12,10,12,11,15,
 13,13,18,18,17,16,17,19,17]