440401920domain: NAppears in sequencesTheta series of D*_21 lattice.at n=37A022074Least number whose number of divisors is n-th term from A014613 (numbers of form p*q*r*s, products of exactly 4 primes, counted with multiplicity).at n=21A061218a(n) = 2^n*binomial(n,2).at n=21A100381Expansion of ((1+x)/(1-2x))^2.at n=23A113070