A031152 Squares composed of digits {2,4,5}.

4, 25, 225, 4225, 55225, 442225, 4545424, 5452225, 42445225, 44422225, 544522225, 2224254244, 4424245225, 4444222225, 4554225225, 54445222225, 55255554225, 444242245225, 444442222225, 5444452222225, 44442422245225, 44444422222225, 544444522222225

Offset: 1

Author

Patrick De Geest

Keywords

• nonn
• base

Comments

Includes all numbers of the form (2*(10^k-1)/3 - 1)^2 for k >= 1, of the form (2*(10^k - 1)/3 - 151)^2 for k >= 4, and of the form (7*(10^k-1)/3 + 4)^2 for k >= 2. - Andrew Howroyd, Oct 18 2024

Links

• Zhao Hui Du, Table of n, a(n) for n = 1..106
• Patrick De Geest, Squares containing at most three distinct digits, Index entries for related sequences

Crossrefs

Cf. A031154.

Programs

Mathematica

Flatten[Table[Select[FromDigits/@Tuples[{2,4,5},n],IntegerQ[Sqrt[#]]&],{n,14}]] (* Harvey P. Dale, Oct 07 2013 *)

Formula

a(n) = A031154(n)^2. - Andrew Howroyd, Oct 18 2024

Extensions

Extended and corrected by author 03/2000.

a(22)-a(23) from Alois P. Heinz, Apr 01 2015