Quarter-squared applied twice.

Terms

a(0) =0a(1) =0a(2) =0a(3) =1a(4) =4a(5) =9a(6) =20a(7) =36a(8) =64a(9) =100a(10) =156a(11) =225a(12) =324a(13) =441a(14) =600a(15) =784a(16) =1024a(17) =1296a(18) =1640a(19) =2025a(20) =2500a(21) =3025a(22) =3660a(23) =4356a(24) =5184a(25) =6084a(26) =7140a(27) =8281a(28) =9604a(29) =11025