Numbers k such that k*(k+4) gives the concatenation of a number m with itself.

Terms

a(0) =7a(1) =97a(2) =451a(3) =546a(4) =689a(5) =854a(6) =997a(7) =4380a(8) =5617a(9) =9997a(10) =72728a(11) =99997a(12) =346531a(13) =653466a(14) =999997a(15) =9090906a(16) =9999997a(17) =94117644a(18) =99999997a(19) =334665331a(20) =336032385a(21) =378253326a(22) =390977440a(23) =439928489a(24) =483516484a(25) =516483513a(26) =560071508