Number of different values assumed by a/b+c/d as a,b,c,d range between 1 and n.

Terms

a(0) =1a(1) =6a(2) =21a(3) =44a(4) =124a(5) =158a(6) =382a(7) =558a(8) =899a(9) =1087a(10) =2022a(11) =2328a(12) =3936a(13) =4542a(14) =5463a(15) =6755a(16) =10366a(17) =11306a(18) =16488a(19) =18315a(20) =21092a(21) =23455a(22) =32562a(23) =34901a(24) =43833a(25) =47945a(26) =56749a(27) =61726a(28) =80278a(29) =83515