login
This site is supported by donations to The OEIS Foundation.

 

Logo

Annual Appeal: Today, Nov 11 2014, is the 4th anniversary of the launch of the new OEIS web site. 70,000 sequences have been added in these four years, all edited by volunteers. Please make a donation (tax deductible in the US) to help keep the OEIS running.

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
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,changed

AUTHOR

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

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Transforms | Superseeker | Recent | More pages
The OEIS Community | Maintained by The OEIS Foundation Inc.

Content is available under The OEIS End-User License Agreement .

Last modified December 19 23:11 EST 2014. Contains 252240 sequences.