Number of elementary sequences of length n.

Terms

a(0) =1a(1) =1a(2) =2a(3) =4a(4) =10a(5) =31a(6) =120a(7) =578a(8) =3422a(9) =24504a(10) =208833a(11) =2086777a(12) =24123293a(13) =318800755a(14) =4766262421a(15) =79874304340