Numbers k such that 2 and 5 occur juxtaposed in the base-10 representation of k but not of k-1.

Terms

a(0) =25a(1) =52a(2) =125a(3) =152a(4) =225a(5) =250a(6) =325a(7) =352a(8) =425a(9) =452a(10) =520a(11) =552a(12) =625a(13) =652a(14) =725a(15) =752a(16) =825a(17) =852a(18) =925a(19) =952a(20) =1025a(21) =1052a(22) =1125a(23) =1152a(24) =1225a(25) =1250a(26) =1325a(27) =1352a(28) =1425a(29) =1452