Area of annuli of consecutive integer thickness.

Terms

a(0) =3a(1) =25a(2) =84a(3) =201a(4) =392a(5) =678a(6) =1077a(7) =1608a(8) =2290a(9) =3141a(10) =4181a(11) =5428a(12) =6902a(13) =8620a(14) =10602a(15) =12867a(16) =15434a(17) =18321a(18) =21548a(19) =25132a(20) =29094a(21) =33451a(22) =38223a(23) =43429a(24) =49087a(25) =55216a(26) =61835a(27) =68964a(28) =76620a(29) =84823