Distance of n-th iteration in an alternating rectangular spiral.

Terms

a(0) =1a(1) =3a(2) =7a(3) =15a(4) =29a(5) =50a(6) =79a(7) =118a(8) =169a(9) =233a(10) =311a(11) =405a(12) =517a(13) =648a(14) =799a(15) =972a(16) =1169a(17) =1391a(18) =1639a(19) =1915a(20) =2221a(21) =2558a(22) =2927a(23) =3330a(24) =3769a(25) =4245a(26) =4759a(27) =5313a(28) =5909a(29) =6548