81721domain: NAppears in sequencesLeast positive k such that 10^n + {k, k+2, k+6, k+8} are all prime.at n=21A121066Number of all polyhedra (tetrahedra of any orientation and octahedra) of any size, formed when intersecting a regular tetrahedron by planes parallel to its sides and dividing its edges into n equal parts.at n=30A216175