A036907 Square refactorable numbers.

1, 9, 36, 225, 441, 625, 1089, 1521, 2025, 2601, 3249, 3600, 4761, 5625, 6561, 7569, 8100, 8649, 10000, 12321, 15129, 16641, 19881, 22500, 25281, 26244, 28224, 31329, 32400, 33489, 35721, 40401, 45369, 47961, 50625, 56169, 62001, 71289, 84681

Offset: 1

Author

Simon Colton (simonco(AT)cs.york.ac.uk)

Keywords

• nonn

Examples

			9 is refactorable because tau(9)=3 and 3 divides 9 and 9 is a square number.
		

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..1000
• S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.
• S. Colton, HR - Automatic Theory Formation in Pure Mathematics

Crossrefs

A033950.

Programs

Mathematica

Select[Range[300]^2,Divisible[#,DivisorSigma[0,#]]&] (* Harvey P. Dale, Nov 21 2020 *)

PARI

isok(n) = issquare(n) && ! (n % numdiv(n)); \\ Michel Marcus, Aug 31 2013