373584043domain: NAppears in sequencesa(n) = n^6 - n^5 + n^4 - n^3 + n^2 - n + 1.at n=27A060888Numbers of the form (3^s+1)/(3^r+1) for s > 1, 1 <= r <= s-1.at n=20A079672a(n) = sigma_6(n^2)/sigma_3(n^2).at n=26A084220a(n) = 3*a(n-1) - a(n-3) + 3*a(n-4), with initial values 0,0,0,1.at n=21A133405