122222222221domain: NAppears in sequencesn times (n 1's): a(n) = n*(10^n - 1)/9.at n=11A053422Expansion of g.f. x*(1+10*x)/((1-x)*(1-10*x^2)).at n=22A094623Expansion of g.f. x*(1+11*x+x^2)/((1-x)*(1+x)*(1-10*x^2)).at n=22A094624a(n) = n 2's sandwiched between two 1's.at n=10A132583