Second column of PE^2.

Terms

a(0) =0a(1) =1a(2) =4a(3) =18a(4) =88a(5) =470a(6) =2724a(7) =17010a(8) =113712a(9) =809262a(10) =6101820a(11) =48540778a(12) =405935688a(13) =3557404838a(14) =32577733972a(15) =310987560930