Ulam's spiral (NNE spoke).

Terms

a(0) =1a(1) =14a(2) =59a(3) =136a(4) =245a(5) =386a(6) =559a(7) =764a(8) =1001a(9) =1270a(10) =1571a(11) =1904a(12) =2269a(13) =2666a(14) =3095a(15) =3556a(16) =4049a(17) =4574a(18) =5131a(19) =5720a(20) =6341a(21) =6994a(22) =7679a(23) =8396a(24) =9145a(25) =9926a(26) =10739a(27) =11584a(28) =12461a(29) =13370