A045859 Numbers whose square has initial digit '5'.

23, 24, 71, 72, 73, 74, 75, 76, 77, 224, 225, 226, 227, 228, 229, 230, 231, 232, 233, 234, 235, 236, 237, 238, 239, 240, 241, 242, 243, 244, 708, 709, 710, 711, 712, 713, 714, 715, 716, 717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, 730

Offset: 1

Author

Jeff Burch

Keywords

• nonn
• base

Comments

A000030(A000290(a(n))) = 5. [Reinhard Zumkeller, Mar 07 2010]

Links

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

Crossrefs

Cf. A045788.

Programs

Mathematica

Rest[Table[If[First[IntegerDigits[n^2]] == 5, n, 0], {n, 1, 2500}]// Union] (* José María Grau Ribas, Feb 15 2010 *)

PARI

isok(n) = digits(n^2)[1] == 5; \\ Michel Marcus, Dec 13 2017