Numbers k such that k concatenated with k-3 gives the product of two numbers which differ by 4.

Terms

a(0) =9a(1) =99a(2) =183a(3) =328a(4) =528a(5) =715a(6) =999a(7) =6099a(8) =9999a(9) =13224a(10) =40495a(11) =99999a(12) =106755a(13) =453288a(14) =999999a(15) =2066115a(16) =2975208a(17) =9999999a(18) =22145328a(19) =28027683a(20) =99999999a(21) =110213248a(22) =110667555a(23) =147928995a(24) =178838403a(25) =226123528a(26) =275074575a(27) =333052608a(28) =378698224a(29) =445332888