1,2
Also number of objects fixed by permutations A057509/A057510 (induced by shallow rotation of general parenthesizations/plane trees).
a(n) = Sum_{d divides n} C(d-1) where C() are the Catalan numbers (A000108).
Occurs for first time in A073202 as row 16. Cf. A057546, A000108.
Sequence in context: A039826 A161746 A045629 this_sequence A110888 A058698 A058699
Adjacent sequences: A034728 A034729 A034730 this_sequence A034732 A034733 A034734
nonn
Erich Friedman (erich.friedman(AT)stetson.edu). More comments from Antti Karttunen (my_firstname.my_surname(AT)iki.fi) Jan 03 2003.
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