Numbers k such that k and k^2 use only the digits 1, 2, 3, 4 and 7.

Terms

a(0) =1a(1) =2a(2) =11a(3) =12a(4) =21a(5) =111a(6) =132a(7) =271a(8) =421a(9) =1111a(10) =1171a(11) =1312a(12) =1332a(13) =2171a(14) =13332a(15) =34311a(16) =34312a(17) =133332a(18) =371111a(19) =417412a(20) =421111a(21) =473421a(22) =1214171a(23) =1333332a(24) =3337271a(25) =3427421a(26) =12137271a(27) =13333332a(28) =121337271a(29) =131423412