124921

Appears in sequences

• Base 9 digits are, in order, the first n terms of the periodic sequence with initial period 2,1,0,3.at n=5A037735
• Triangle T(n, k) read by rows; given by [1, 2, 3, 4, 5, 6, ..] DELTA [1, 4, 9, 16, 25, 36, ...] where DELTA is the operator defined in A084938.at n=19A086872
• Triangle read by rows: T(n,k) is the number of down-up permutations on [n] with k left-to-right maxima.at n=31A098906
• Number of intersections of diagonals in the interior and exterior of a regular n-gon.at n=33A211383
• Number of (w,x,y,z) with all terms in {0,...,n} and w=max{w,x,y,z}-min{w,x,y,z}; i.e., the range of (w,x,y,z) is its first term.at n=40A212744
• Place n points in general position on each side of an equilateral triangle, and join every pair of the 3*n+3 boundary points by a chord; sequence gives number of regions in the resulting planar graph.at n=15A367118