a(n) is the surface area of the stepped pyramid with n levels described in A245092.

Terms

a(0) =6a(1) =20a(2) =40a(3) =70a(4) =102a(5) =150a(6) =194a(7) =256a(8) =318a(9) =394a(10) =462a(11) =566a(12) =646a(13) =750a(14) =858a(15) =984a(16) =1088a(17) =1238a(18) =1354a(19) =1518a(20) =1666a(21) =1826a(22) =1966a(23) =2182a(24) =2344a(25) =2532a(26) =2720a(27) =2944a(28) =3120a(29) =3384