S_{2,1}(n, y) = ∫_{0}^{+∞} x^{n}W_{2}(x, y)dx  (1)

B_{r,s}(n, y) = ∑_{k=0}^{∞} S_{r,s}(n, k)y^{k}  (2)

B(n) = ∫_{0}^{+∞} x^{n}W (x)dx  (3)

B_{F} (n, y) = ∫_{0}^{+∞} x^{n}W_{F} (x, y)dx  (4)

B_{G}(n, y) = ∫_{0}^{+∞} x^{n}W_{G}(x, y)dx  (5)

W_{F G}(x, y) = ∫_{0}^{+∞} W_{F} (x, z)W_{G}(z, y)dz  (6)