Squares formed by concatenating k and 2*k+1.

Terms

a(0) =25a(1) =49a(2) =1225a(3) =4489a(4) =112225a(5) =444889a(6) =11122225a(7) =44448889a(8) =816416329a(9) =1111222225a(10) =1451229025a(11) =3832476649a(12) =4444488889a(13) =111112222225a(14) =444444888889