20901

Appears in sequences

• Numbers k such that the continued fraction for sqrt(k) has even period and if the last term of the periodic part is deleted the central term is 96.at n=31A031594
• Invariant number of polygons of n-circum-C_5 H_5 systems.at n=9A122678
• Number of ways to place zero or more nonadjacent 0,0 1,0 2,1 3,1 4,1 5,2 6,2 polyhexes in any orientation on a planar nXnXn triangular grid.at n=7A155345
• Partial sums of A138202.at n=26A164940
• a(0) = 0 and a(n) = (4*n^3 - 12*n^2 + 20*n - 9)/3 for n >= 1.at n=26A174794
• Define a pair of sequences c_n, d_n by c_0=0, d_0=1 and thereafter c_n = c_{n-1}+d_{n-1}, d_n = c_{n-1}+4*n+2; sequence here is d_n.at n=17A192750
• Number of zero-sum -n..n arrays of 4 elements with adjacent element differences also in -n..n.at n=21A202254
• Expansion of 1/2 - (1/2)*(sqrt((2*sqrt(-3*x^2 - 2*x + 1) + 3*x - 2)/x)).at n=9A243255
• Partial sums of A255283.at n=50A255428