Numbers k such that k and k^2 use only the digits 0, 2, 5 and 7.

Terms

a(0) =0a(1) =5a(2) =50a(3) =500a(4) =505a(5) =755a(6) =5000a(7) =5005a(8) =5050a(9) =7550a(10) =50000a(11) =50005a(12) =50050a(13) =50500a(14) =50505a(15) =75500a(16) =500000a(17) =500005a(18) =500050a(19) =500500a(20) =500505a(21) =500755a(22) =505000a(23) =505050a(24) =755000a(25) =5000000a(26) =5000005a(27) =5000050a(28) =5000500a(29) =5000505