Expansion of e.g.f. tan(tan(tan(x))).A003720Expansion of e.g.f. tan(tan(tan(x))).Terms a(0) =1a(1) =6a(2) =168a(3) =10672a(4) =1198080a(5) =208521728a(6) =51874413568External referencesoeis: A003720