Zarankiewicz's problem k_2(n).

Terms

a(0) =4a(1) =7a(2) =10a(3) =13a(4) =17a(5) =22a(6) =25a(7) =30a(8) =35a(9) =40a(10) =46a(11) =53a(12) =57a(13) =62a(14) =68a(15) =75a(16) =82a(17) =89a(18) =97a(19) =106a(20) =109a(21) =116a(22) =123