151218

Appears in sequences

• Describe the n-th triangular number A000217(n).at n=32A045986
• Matrix square of triangle A104980.at n=28A104988
• Number of lower triangles of a 4 X 4 0..n array with no element differing from any of its horizontal or vertical neighbors by more than one.at n=22A194933
• Number of (n+1)X(n+1) -6..6 symmetric matrices with every 2X2 subblock having sum zero and two, three or four distinct values.at n=4A211260