A036907 - OEIS

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

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

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

EXAMPLE

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

MATHEMATICA

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

PROG

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

CROSSREFS

A033950.

Sequence in context: A094973 A038780 A073984 * A027381 A335783 A024120

Adjacent sequences: A036904 A036905 A036906 * A036908 A036909 A036910

KEYWORD

nonn

AUTHOR

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

STATUS

approved