a(n) = (7*n+2)^2.

Terms

a(0) =4a(1) =81a(2) =256a(3) =529a(4) =900a(5) =1369a(6) =1936a(7) =2601a(8) =3364a(9) =4225a(10) =5184a(11) =6241a(12) =7396a(13) =8649a(14) =10000a(15) =11449a(16) =12996a(17) =14641a(18) =16384a(19) =18225a(20) =20164a(21) =22201a(22) =24336a(23) =26569a(24) =28900a(25) =31329a(26) =33856a(27) =36481a(28) =39204a(29) =42025