A045856 Numbers whose square has initial digit '2'.

5, 15, 16, 17, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172, 173, 448, 449, 450, 451, 452, 453, 454, 455, 456

Offset: 1

Author

Jeff Burch

Keywords

• nonn
• base

Links

• Seiichi Manyama, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A045785

Programs

Mathematica

Select[Range[500],IntegerDigits[#^2][[1]]==2&] (* Harvey P. Dale, Apr 15 2024 *)

PARI

isok(n) = digits(n^2)[1] == 2; \\ Michel Marcus, May 28 2017

Extensions

Corrected by Seiichi Manyama, May 28 2017