Basis for code in A075940.

Terms

a(0) =255a(1) =3855a(2) =13107a(3) =21845a(4) =38505a(5) =197462a(6) =329059a(7) =591418a(8) =1118584a(9) =2167325a(10) =4265038a(11) =8460068a(12) =251658255a(13) =855638067a(14) =1426063445a(15) =2516582505a(16) =12935233622a(17) =21558722659a(18) =38755369018a(19) =73299656824a(20) =142035910685