a(n) = sqrt(6*A138288(n)^2 - 2).

Terms

a(0) =2a(1) =22a(2) =218a(3) =2158a(4) =21362a(5) =211462a(6) =2093258a(7) =20721118a(8) =205117922a(9) =2030458102a(10) =20099463098a(11) =198964172878