Numbers k such that k and k^2 use only the digits 1, 2, 5, 7 and 9.

Terms

a(0) =1a(1) =5a(2) =11a(3) =15a(4) =27a(5) =77a(6) =227a(7) =527a(8) =715a(9) =1515a(10) =1711a(11) =2777a(12) =7227a(13) =7715a(14) =22715a(15) =52915a(16) =71911a(17) =97527a(18) =159911a(19) =275527a(20) =277977a(21) =715511a(22) =727511a(23) =977511a(24) =2791515a(25) =7219777a(26) =7557511a(27) =7715515a(28) =7727711a(29) =7727715