a(n) is the concatenation of a(n-1) and a(n-2) with a(1)=1, a(2)=2.

A008351

a(n) is the concatenation of a(n-1) and a(n-2) with a(1)=1, a(2)=2.

Terms

    a(0) =1a(1) =2a(2) =21a(3) =212a(4) =21221a(5) =21221212

External references