8346320domain: NAppears in sequencesa(0)=0, a(1)=4; for n > 1, a(n) = 18*a(n-1) - a(n-2) + 8.at n=6A132584Expansion of x^2*(1+x^2) / ( (x^2-x+1)*(-x^2-x+1)*(1+x+x^2) ).at n=36A227047Numbers k such that k and k+1 are both antiharmonic numbers (A020487).at n=15A335389