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A036897 Square root of odd refactorable numbers. 4
1, 3, 15, 21, 25, 33, 39, 45, 51, 57, 69, 75, 81, 87, 93, 111, 123, 129, 141, 159, 177, 183, 189, 201, 213, 219, 225, 237, 249, 267, 291, 303, 309, 315, 321, 327, 339, 343, 381, 393, 405, 411, 417, 447, 453, 471, 489, 495, 501, 519, 525, 537, 543, 567, 573 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

Odd refactorable numbers are always squares.

LINKS

Table of n, a(n) for n=1..55.

S. Colton, Refactorable Numbers - A Machine Invention, J. Integer Sequences, Vol. 2, 1999, #2.

S. Colton, HR - Automatic Theory Formation in Pure Mathematics

EXAMPLE

15^2 is refactorable because 225 has 9 divisors and 9 divides 225.

PROG

(PARI) isrefac(n) = ! (n % numdiv(n));

lista(nn) = {forstep (n = 1, nn, 2, if (isrefac(n), print1(sqrtint(n), ", ")); ); } \\ Michel Marcus, Aug 31 2013

CROSSREFS

Cf. A033950.

Sequence in context: A048087 A001897 A074214 * A129966 A243128 A216521

Adjacent sequences:  A036894 A036895 A036896 * A036898 A036899 A036900

KEYWORD

nonn

AUTHOR

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

STATUS

approved

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Last modified December 10 15:13 EST 2016. Contains 279003 sequences.