Number of n-celled polyominoes which are of square type.

Terms

a(0) =1a(1) =0a(2) =1a(3) =1a(4) =6a(5) =7a(6) =25a(7) =80a(8) =255a(9) =795a(10) =2919a(11) =10378a(12) =36590a(13) =130716a(14) =480773a(15) =1774714a(16) =6543633a(17) =24208803a(18) =90331307a(19) =339178346a(20) =1277308160a(21) =4819109576