Number of distributive lattices; also number of paths with n turns when light is reflected from 4 glass plates.

A006357

Number of distributive lattices; also number of paths with n turns when light is reflected from 4 glass plates.

Terms

    a(0) =1a(1) =4a(2) =10a(3) =30a(4) =85a(5) =246a(6) =707a(7) =2037a(8) =5864a(9) =16886a(10) =48620a(11) =139997a(12) =403104a(13) =1160693a(14) =3342081a(15) =9623140a(16) =27708726a(17) =79784098a(18) =229729153a(19) =661478734a(20) =1904652103a(21) =5484227157a(22) =15791202736a(23) =45468956106a(24) =130922641160a(25) =376976720745

External references