For positive integers a, b and integers x, y such that S = a³ + b³ = x³ + y³, we prove that x+y ≡ a+b (mod 6); moreover, we give a parametric function r_i → (x(r_i),y(r_i)) with (x(r_i))³ + (y(r_i))³ = a³ + b³ for chosen parameters r_i, and we conjecture that most such S are multiples of 18 if S is large enough. Accordingly, floating sieving is introduced and upper bounds on the Cabtaxi numbers Ca(n) with 43 ≤ n ≤ 57, and the Taxicab numbers Ta(n) with n = 23,24 are given. Among them, Ta(n) with n = 23,24, and Ca(n) with n = 43,44, are included in the On-Line Encyclopedia of Integer Sequences.