Increase in the number of free polyominoes from order n to n+1.

Terms

a(0) =0a(1) =0a(2) =1a(3) =3a(4) =7a(5) =23a(6) =73a(7) =261a(8) =916a(9) =3370a(10) =12418a(11) =46527a(12) =174991a(13) =663380a(14) =2524605a(15) =9652679a(16) =37028654a(17) =142514143a(18) =550002180a(19) =2128047718a(20) =8252388728a(21) =32068797010a(22) =124855150040a(23) =486952692675