A279420 Numbers k such that k^2 has an odd number of digits and the middle digit is 0.

10, 20, 30, 100, 105, 138, 145, 155, 179, 195, 200, 205, 217, 226, 241, 243, 245, 247, 249, 251, 253, 255, 257, 259, 274, 283, 295, 300, 305, 1000, 1005, 1010, 1015, 1020, 1025, 1030, 1049, 1054, 1068, 1082, 1091, 1100, 1114, 1127, 1136, 1149, 1158, 1162, 1175

Offset

1,1

Links

Lars Blomberg, Table of n, a(n) for n = 1..10000

Example

10^2 = 1(0)0, 195^2 = 38(0)25, 1000^2 = 100(0)000.
The sequences of squares starts: 100, 400, 900, 10000, 11025, 19044, 21025, 24025, 32041, 38025, 40000, ...

Mathematica

Select[Range@ 1175, Function[w, And[OddQ@ Length@ w, First@ Take[w, {Ceiling[Length[w]/2]}] == 0]]@ IntegerDigits[#^2] &] (* Michael De Vlieger, Dec 12 2016 *)

Prog

(PARI) isok(n) = my(d=digits(n^2)); (#d % 2) && (d[#d\2 + 1] == 0); \\ Michel Marcus, Dec 18 2016

Crossrefs

Cf. A279421-A279429.

Sequence in context: A355695 A273016 A269238 * A274051 A345069 A187712

Adjacent sequences: A279417 A279418 A279419 * A279421 A279422 A279423

Keyword

nonn,base,easy

Author

Lars Blomberg, Dec 12 2016

Status

approved