Sum of indices of windows of trapezoidal maps.

Terms

a(0) =1a(1) =1a(2) =1a(3) =4a(4) =9a(5) =27a(6) =89a(7) =304a(8) =944a(9) =3259a(10) =11081a(11) =38044a(12) =132921a(13) =467771a(14) =1650279a(15) =5907280a(16) =21183657a(17) =76488912a(18) =277631065a(19) =1012588940a(20) =3707127319a(21) =13632296219a(22) =50292158921a(23) =186165033296a(24) =691181554768