Number of fixed polyominoes with n cells of which no four are equally spaced on a straight line.

Terms

a(0) =1a(1) =2a(2) =6a(3) =17a(4) =45a(5) =114a(6) =264a(7) =545a(8) =1061a(9) =2070a(10) =3990a(11) =7275a(12) =12556a(13) =20824a(14) =33584a(15) =52753a(16) =80560a(17) =119274a(18) =170168a(19) =232700a(20) =306472a(21) =396580a(22) =517300a(23) =688736a(24) =926816a(25) =1241720a(26) =1640968a(27) =2130448a(28) =2710356a(29) =3383596