41244

Appears in sequences

• a(n) is the number of subsets of {1,...,n} containing no solutions to x+y=z with x and y distinct (one version of "sum-free subsets").at n=22A085489
• Triangle read by rows: coefficients of polynomials arising in the spontaneous magnetization of the anisotropic square lattice Ising model (see pp. 174-5 of the Guttmann reference).at n=30A138781
• Expansion of 1/(1-2*x-3*x^2+x^4) in powers of x.at n=10A201967
• Place two n-gons with radii 1 and 2 concentrically, forming an annular area between them. Connect all the vertices with line segments that lie entirely within that area. Then a(n) is the number of edges in that figure.at n=25A337702