0,4

Nonisomorphic closed meanders, where two closed meanders are considered equivalent if one can be obtained from the other by reflections in an East-West or North-South mirror (a group of order 4).

A meander can be specified by marking 2n equally spaced points along a line, and recording the order in which the meander visits the points.

For n = 2, 4, 6, 8 the solutions are as follows:

n=2: 1 2

n=4: 1 2 3 4

n=6: 1 2 3 4 5 6, 1 2 3 6 5 4, 1 2 5 4 3 6

n=8: 1 2 3 4 5 6 7 8, 1 2 3 4 5 8 7 6, 1 2 3 4 7 6 5 8, 1 2 7 6 3 4 5 8, 1 2 3 6 7 8 5 4, 1 2 3 6 5 4 7 8, 1 2 7 6 5 4 3 8, 1 2 3 8 5 6 7 4, 1 2 3 8 7 4 5 6, 1 2 5 6 7 4 3 8, 1 2 7 4 5 6 3 8, 1 4 3 2 7 6 5 8

The total number of closed meanders with 2n crossings is given in A005315. Cf. A077055, A078104, A078105, A078591.

Sequence in context: A102078 A113341 A125862 this_sequence A001205 A112320 A103366

Adjacent sequences: A077457 A077458 A077459 this_sequence A077461 A077462 A077463

nonn,nice

njas and Jon Wild (wild(AT)music.mcgill.ca), Dec 03 2002