A055859 a(n) and floor(a(n)/7) are both squares; i.e., squares which remain squares when written in base 7 and last digit is removed.

0, 1, 4, 9, 64, 256, 2025, 16129, 64516, 514089, 4096576, 16386304, 130576329, 1040514049, 4162056196, 33165873225, 264286471744, 1057145886976, 8424001222569, 67127723308801, 268510893235204, 2139663144659049, 17050177433963584, 68200709735854336

Offset: 1

Author

Henry Bottomley, Jul 14 2000

Keywords

• base
• nonn

Comments

Square roots of a(n) are listed in A204516, square roots of floor(a(n)/7) in A204517. - M. F. Hasler, Jan 16 2012

Examples

			a(5) = 256 because 256 = 16^2 = 514 base 7 and 51 base 7 = 36 = 6^2.
		

Links

• M. F. Hasler, Truncated squares, OEIS wiki, Jan 16 2012
• Index to sequences related to truncating digits of squares.

Crossrefs

Cf. A023110.

Formula

a(n) = A204516(n)^2. - M. F. Hasler, Jan 16 2012

Empirical g.f.: -x^2*(9*x^8+256*x^7+64*x^6-270*x^5-764*x^4-191*x^3+9*x^2+4*x+1) / ((x-1)*(x^2+x+1)*(x^6-254*x^3+1)). - Colin Barker, Sep 15 2014