Number of unit square lattice cells enclosed by origin centered circle of diameter 2n+1.

Terms

a(0) =0a(1) =4a(2) =12a(3) =24a(4) =52a(5) =76a(6) =112a(7) =148a(8) =192a(9) =256a(10) =308a(11) =376a(12) =440a(13) =524a(14) =608a(15) =688a(16) =796a(17) =904a(18) =1012a(19) =1124a(20) =1232a(21) =1372a(22) =1508a(23) =1648a(24) =1788a(25) =1952a(26) =2112a(27) =2268a(28) =2448a(29) =2616