276388

Appears in sequences

• Number of permutations of length n which avoid the patterns 1234, 1324, 3421.at n=17A116829
• Place n equally spaced points on each side of an equilateral triangle, and join each of these points by a chord to the 2*n new points on the other two sides: sequence gives number of vertices in the resulting planar graph.at n=20A366483