Downward vertical of triangular spiral in A051682.

Terms

a(0) =1a(1) =25a(2) =85a(3) =181a(4) =313a(5) =481a(6) =685a(7) =925a(8) =1201a(9) =1513a(10) =1861a(11) =2245a(12) =2665a(13) =3121a(14) =3613a(15) =4141a(16) =4705a(17) =5305a(18) =5941a(19) =6613a(20) =7321a(21) =8065a(22) =8845a(23) =9661a(24) =10513a(25) =11401a(26) =12325a(27) =13285a(28) =14281a(29) =15313