53721

Appears in sequences

• Number of ways, counted up to symmetry, to build a contiguous building with n LEGO blocks of size 1 X 7 which is flat, i.e., with all blocks in parallel position, and symmetric after a rotation by 180 degrees.at n=9A123805
• Number of zero-sum -n..n arrays of 4 elements with first and second differences also in -n..n.at n=36A201875
• a(n) = number of segments (edges) in the configuration A290447(n).at n=30A290866
• a(0) = 0, a(1) = 1. For n >= 2, a(n) = a(n-1)/(n-1) if n-1 divides a(n-1); otherwise, a(n) = a(n-1) + a(n-2).at n=42A343376