Ulam's spiral (NNW spoke).

Terms

a(0) =1a(1) =16a(2) =63a(3) =142a(4) =253a(5) =396a(6) =571a(7) =778a(8) =1017a(9) =1288a(10) =1591a(11) =1926a(12) =2293a(13) =2692a(14) =3123a(15) =3586a(16) =4081a(17) =4608a(18) =5167a(19) =5758a(20) =6381a(21) =7036a(22) =7723a(23) =8442a(24) =9193a(25) =9976a(26) =10791a(27) =11638a(28) =12517a(29) =13428