a(n)*Pi is the total length of irregular spiral (center points: 1, 2, 3, 4) after n rotations.

Terms

a(0) =3a(1) =6a(2) =17a(3) =28a(4) =47a(5) =66a(6) =93a(7) =120a(8) =155a(9) =190a(10) =233a(11) =276a(12) =327a(13) =378a(14) =437a(15) =496a(16) =563a(17) =630a(18) =705a(19) =780a(20) =863a(21) =946a(22) =1037a(23) =1128a(24) =1227a(25) =1326a(26) =1433a(27) =1540a(28) =1655a(29) =1770