206821

Properties

Appears in sequences

• Numbers k such that 209*2^k+1 is prime.at n=21A032481
• Number of ways to place zero or more nonadjacent 0,0 1,0 2,1 2,2 3,0 3,1 4,2 5,2 polyhexes in any orientation on a planar nXnXn triangular grid.at n=9A155406
• Prime numbersat n=18534