a(n) = Sum_{-n<i<n, -n<j<n, gcd{i,j}=2} (n-|i|)*(n-|j|).

Terms

a(0) =0a(1) =0a(2) =16a(3) =48a(4) =120a(5) =224a(6) =424a(7) =688a(8) =1096a(9) =1600a(10) =2392a(11) =3344a(12) =4568a(13) =5984a(14) =7976a(15) =10256a(16) =13112a(17) =16320a(18) =20360a(19) =24848a(20) =30136a(21) =35936a(22) =43208a(23) =51152a(24) =60184a(25) =69952a(26) =81800a(27) =94576a(28) =109000a(29) =124448