Rectangular free polyominoes: number of n-celled polyominoes when the cell is a rectangle.

A056780

Rectangular free polyominoes: number of n-celled polyominoes when the cell is a rectangle.

Terms

    a(0) =1a(1) =2a(2) =3a(3) =9a(4) =21a(5) =68a(6) =208a(7) =730a(8) =2542a(9) =9287a(10) =34053a(11) =127112a(12) =476849a(13) =1803636a(14) =6851960a(15) =26157362a(16) =100211446a(17) =385239872a(18) =1485232325a(19) =5741327939a(20) =22246061118a(21) =86383655207a(22) =336093789246

External references