Numbers k such that k * (k + 7) is the concatenation of a number m with itself.

Terms

a(0) =4a(1) =94a(2) =455a(3) =539a(4) =994a(5) =7665a(6) =9994a(7) =72721a(8) =99994a(9) =356429a(10) =643565a(11) =999994a(12) =9090910a(13) =9999994a(14) =35294118a(15) =64705876a(16) =99999994a(17) =335664329a(18) =664335665a(19) =684210520a(20) =818181819a(21) =838056674a(22) =846153847a(23) =866028702a(24) =980125139a(25) =999999994