Problem 156. Parasitic numbers

Created by the cyclist

Solve Later

{"relationships":[{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/document","targetMode":"","relationshipId":"rId1","target":"/matlab/document.xml"},{"relationshipType":"http://schemas.mathworks.com/matlab/code/2013/relationships/output","targetMode":"","relationshipId":"rId2","target":"/matlab/output.xml"}],"parts":[{"partUri":"/matlab/document.xml","relationship":[],"contentType":"application/vnd.mathworks.matlab.code.document+xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n<w:document xmlns:w=\"http://schemas.openxmlformats.org/wordprocessingml/2006/main\"><w:body><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Test whether the first input x is an n-parasitic number:</w:t></w:r><w:r><w:t> </w:t></w:r><w:hyperlink w:docLocation=\"http://en.wikipedia.org/wiki/Parasitic_number\"><w:r><w:t>http://en.wikipedia.org/wiki/Parasitic_number</w:t></w:r></w:hyperlink><w:r><w:t>. (</w:t></w:r><w:r><w:t> </w:t></w:r><w:r><w:rPr><w:i/></w:rPr><w:t>n</w:t></w:r><w:r><w:t> is the second input.)</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>Examples:</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>parasitic(128205,4) ---&gt; true</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>parasitic(179487,4) ---&gt; true</w:t></w:r></w:p><w:p><w:pPr><w:pStyle w:val=\"text\"/></w:pPr><w:r><w:t>parasitic(179487,3) ---&gt; false</w:t></w:r></w:p></w:body></w:document>"},{"partUri":"/matlab/output.xml","contentType":"text/xml","content":"<?xml version=\"1.0\" encoding=\"UTF-8\" standalone=\"no\" ?><embeddedOutputs><metaData><evaluationState>manual</evaluationState><layoutState>code</layoutState><outputStatus>ready</outputStatus></metaData><outputArray type=\"array\"/><regionArray type=\"array\"/></embeddedOutputs>"}]}

Solve

Solution Stats

557 Solutions
275 Solvers

Last Solution submitted on Mar 20, 2023

Last 200 Solutions

Problem Comments

5 Comments

5 Comments

Show 2 older comments

@bmtran (Bryant Tran) on 1 Feb 2012

might be best to add a test case to guard against test suite hacking

John D'Errico on 30 Sep 2016

Far too few test cases. In fact, a serious issue with this problem is that there are too few parasitic numbers that will fit into even 64 bits for most values of n.

John D'Errico on 30 Sep 2016

I've added some test cases, that will make it a bit more difficult to game this problem.

JD on 7 Nov 2016

Cases 5 and 7 are identical, and I believe they are both wrong. 5 x 142857 = 714285. Isn't this a parasitic number? What am I missing?

Jess Stuart on 8 Feb 2017

Can the problem creator disqualify "solutions" that cheat? There should be a point penalty (-200) associated with cheating too.

Solution Comments

Solution 1047166

5 Comments

5 Comments

Show 2 older comments

JD on 7 Nov 2016

Cases 5 and 7 are identical, and I believe they are both wrong. 5 x 142857 = 714285. Isn't this a parasitic number? What am I missing?

Jan Orwat on 8 Nov 2016

There is 4, not 5

JD on 8 Nov 2016

I mis-typed. 4 x 142857 = 571428, which is a shift right of 2. Incidentally, both n = 4 and 5 both make parasitic pairs with 142857.

Jan Orwat on 8 Nov 2016

Thus it is not a 4-parasitic number. It doesn't meet the definition. Nevertheless is a great example of a cyclic number. You can get different cyclic permutations when multiply 142857 by 1, 2, 3, 4, 5 and 6. For 5 you got shift by one digit, therefore it's 5-parasitic.

JD on 9 Nov 2016

Ahhh, I see! Thanks, Jan - I get it now!

Solution 13122

1 Comment

1 Comment

the cyclist on 29 Jan 2012

Not actually a general solution. Takes advantage of limited test cases.

Problem Recent Solvers275

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Problem 156. Parasitic numbers

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers275

Suggested Problems

More from this Author23

Problem Tags

Community Treasure Hunt

Problem 156. Parasitic numbers

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers275

Suggested Problems

More from this Author23

Problem Tags

Community Treasure Hunt

Players