1050880domain: NAppears in sequencesNumbers k that divide the (left) concatenation of all numbers <= k written in base 21 (most significant digit on left).at n=20A029490Dirichlet convolution of b_n=2^(n-1) with itself.at n=19A034733a(n) = Sum_{d|n} 2^d*phi(2*n/d).at n=19A306898