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

Author

Lars Blomberg, Dec 12 2016

Keywords

• nonn
• base
• easy

Examples

			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, ...
		

Links

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

Crossrefs

Cf. A279421-A279429.

Programs

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 *)
Select[Range[1200],With[{len=IntegerLength[#^2]},OddQ[len]&&IntegerDigits[#^2][[(len+1)/2]]==0&]] (* Harvey P. Dale, Mar 29 2025 *)

PARI

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