Analog of A113869 for three generators.

Terms

a(0) =1a(1) =0a(2) =-1a(3) =0a(4) =-3a(5) =-6a(6) =-38a(7) =-186a(8) =-1181a(9) =-8094a(10) =-61865a(11) =-516702a(12) =-4688020a(13) =-45887352a(14) =-481954769a(15) =-5406249972a(16) =-64506680939a(17) =-815807306442