a(n) = 5*(10^(2*n+1) - 1)/9 - 4*10^n.A332151a(n) = 5*(10^(2*n+1) - 1)/9 - 4*10^n.Terms a(0) =1a(1) =515a(2) =55155a(3) =5551555a(4) =555515555a(5) =55555155555External referencesoeis: A332151