A078592 Call two meanders from A005316 with 2n crossings equivalent if they differ by reflections in the X or Y axes. Sequence gives number of inequivalent meanders.

1, 1, 2, 8, 42, 273, 1970, 15368, 126510, 1086546, 9652364, 88172609, 824506191, 7865294687, 76331857094, 751981532942, 7506432993145, 75811326673326, 773682540353704, 7969986193751019, 82798726340037900, 866804540900696571

Offset: 0

Author

N. J. A. Sloane and Jon Wild, Dec 08 2002

Keywords

• nonn

Comments

Symmetry group has order 4.

Links

• Jean-François Alcover, Table of n, a(n) for n = 0..27

Programs

Mathematica

A005316 = Cases[Import["https://oeis.org/A005316/b005316.txt", "Table"], {, }][[All, 2]];
a[n_] := (A005316[[2 n + 1]] + A005316[[n + 1]])/2;
a /@ Range[0, 27] (* Jean-François Alcover, Sep 20 2019 *)

Formula

a(n) = (A005316(2n)+A005316(n))/2.