Sequences

Antichains (or order ideals) in the poset 2*2*3*n or size of the distributive lattice J(2*2*3*n).

Antichains (or order ideals) in the poset 2*2*4*n or size of the distributive lattice J(2*2*4*n).

Antichains (or order ideals) in the poset 2*2*5*n or size of the distributive lattice J(2*2*5*n).

Number of antichains (or order ideals) in the poset B_4 X [n]; or size of the distributive lattice J(B_4 X [n]).

Numbers k with an even number of 1's in binary, ignoring last bit.

Number of binary tree partitions.

Number of cyclically symmetric plane partitions in the n-cube; also number of 2n X 2n half-turn symmetric alternating sign matrices divided by number of n X n alternating sign matrices.

Number of binary vectors of length n+1 beginning with 0 and containing just 1 singleton.

The "amusical permutation" of the nonnegative numbers: a(2n)=3n, a(4n+1)=3n+1, a(4n-1)=3n-1.

a(n) = 2*n/3 for n divisible by 3, otherwise a(n) = round(4*n/3). Or, equivalently, a(3*n-2) = 4*n-3, a(3*n-1) = 4*n-1, a(3*n) = 2*n.

The Collatz or 3x+1 map: a(n) = n/2 if n is even, 3n + 1 if n is odd.

Number of positive definite reduced binary quadratic forms of discriminant -A014601(n).

Numbers of terms in expressions for coefficients of "Lovelock Lagrangians" (or "Gauss-Bonnet forms") in terms of Riemann-Christoffel curvature tensor and two of its contractions (viz., the Ricci curvature tensor and the Riemann curvature scalar) for n-dimensional differentiable manifolds having a general linear connection.

Numbers of terms in expressions for coefficients of Euler-Lagrange tensors in terms of Riemann-Christoffel curvature tensor and two of its contractions (viz., the Ricci curvature tensor and the Riemann curvature scalar) for n-dimensional differentiable manifolds having a general linear connection.

Number of positive definite reduced binary quadratic forms of discriminant -4*n.

Number of equivalence classes of cycles (or periods) of reduced indefinite binary quadratic forms of determinant -n (see comments).

Number of indecomposable positive definite ternary quadratic forms of determinant n.

Determinants of indecomposable indefinite ternary quadratic forms.

Prime self (or Colombian) numbers: primes not expressible as the sum of an integer and its digit sum.

Number of noncyclic (finite) simple groups with n conjugacy classes.

Number of equivalence classes of 4 X n binary matrices when one can permute rows, permute columns and complement columns.

Number of n X 3 binary matrices under row and column permutations and column complementations.

Number of n X 4 binary matrices under row and column permutations and column complementations.

Number of equivalence classes of n X n binary matrices when one can permute rows, permute columns and complement columns.

Number of sensed planar maps with n edges.

Number of unsensed planar maps with n edges.

Number of sensed genus 1 maps with n edges.

Number of unsensed genus 1 maps with n edges.

Number of sensed planar maps with n edges and without faces of degree 1.

Number of unsensed planar maps with n edges and without faces of degree 1.

Number of sensed loopless planar maps with n edges.

Number of unsensed loopless planar maps with n edges.

Number of sensed planar maps with n edges and without faces of degree 1 or 2.

Number of unsensed planar maps with n edges and without faces of degree 1 or 2.

Number of sensed planar maps with n edges and without loops or parallel edges.

Number of unsensed planar maps with n edges and without loops or parallel edges.

Number of sensed planar maps with n edges and without faces or vertices of degree 1.

Number of unsensed planar maps with n edges and without faces or vertices of degree 1.

Number of sensed planar maps with n edges and without loops or isthmuses.

Number of unsensed planar maps with n edges and without loops or isthmuses.

Number of sensed simple planar maps with n edges and without vertices of degree 1.

Number of unsensed simple planar maps with n edges and without vertices of degree 1.

Number of sensed 2-connected (nonseparable) planar maps with n edges.

Number of unsensed 2-connected planar maps with n edges.

Number of sensed 2-connected maps with n edges and without faces of degree 2.

Number of unsensed 2-connected maps with n edges and without faces of degree 2.

Number of sensed 2-connected simple planar maps with n edges.

Number of unsensed 2-connected simple planar maps with n edges.

Number of nonseparable rooted toroidal maps with n + 3 edges and n + 1 vertices.

Number of nonseparable rooted toroidal maps with n + 4 edges and n + 1 vertices.