a(n) = 4*n*(n+1) + 3.

Terms

a(0) =3a(1) =11a(2) =27a(3) =51a(4) =83a(5) =123a(6) =171a(7) =227a(8) =291a(9) =363a(10) =443a(11) =531a(12) =627a(13) =731a(14) =843a(15) =963a(16) =1091a(17) =1227a(18) =1371a(19) =1523a(20) =1683a(21) =1851a(22) =2027a(23) =2211a(24) =2403a(25) =2603a(26) =2811a(27) =3027a(28) =3251a(29) =3483