Why does Select does not work with PrimeQ?

Questions
1

Hi,

Select[{1, 2, 6, 15, 37, 90, 218, 527, 1273, 3074}, EvenQ]

as well as

Select[{1, 2, 6, 15, 37, 90, 218, 527, 1273, 3074}, OddQ]

do work as expected.

Why does PrimeQ does not work the same way?
Wolfram alpha link to sample

Hermann.

2

In[1]:= Select[{1, 2, 6, 15, 37, 90, 218, 527, 1273, 3074}, PrimeQ]

Out[1]= {2, 37}
3

Thanks for showing that it works in general.

What I stated is that it does not work in Wolfram Alpha link:

http://www.wolframalpha.com/input/?i=Select%5B%7B1,%202,%206,%2015,%2037,%2090,%20218,%20527,%201273,%203074%7D,%20PrimeQ%5D

While eg. OddQ does work in Wolram Alpha link:

http://www.wolframalpha.com/input/?i=Select%5B%7B1%2C+2%2C+6%2C+15%2C+37%2C+90%2C+218%2C+527%2C+1273%2C+3074%7D%2C+OddQ%5D

So is PrimeQ not working in Wolfram Alpha link a Wolfram Alpha bug?

Hermann.

4

Well, Wolfram|Alpha is not Mathematica and in general, Mathematica syntax does not work with it. W|A has a natural language interface, which makes it possible to ask questions without learning a programming language. But it can also be very frustrating to get it to do what you want (at least I find it very frustrating and unpredictable).

Try telling it to

select primes from {1, 2, 6, 15, 37, 90, 218, 527, 1273, 3074}

Based on the interpretation of this natural language query above, I tried

Select[{1, 2, 6, 15, 37, 90, 218, 527, 1273, 3074}, PrimeQ[#1]&]

which also works.

5

Thank you, both terms work in Wolfram|Alpha.

And you are right, the natual language interpretation is strange sometimes as this link shows:

select primes from LinearRecurrence[{0,7,0,-7,0,1},{1,2,6,15,37,90},20]

Should have returned the same as your terms, but does something completely different.

I really like Wolfram|Alpha for two reasons:

  • its free
  • you can easily share link for an evaluation

I know Mathematica is free for Raspberry Pi, but is some “more Mathematica like” web interface than Wolfram/Alpha out there?

Hermann.

6

I know Mathematica is free for Raspberry Pi, but is some “more Mathematica like” web interface than Wolfram/Alpha out there?

Yes, there is. Take a look at the Programming Cloud. It can be used with a free account, with some limitations. I haven’t looked at it in detail as I do have access to desktop Mathematica, so I’m not sure how severe the limitations are, but on a first glance it appears to be a pretty complete Mathematica-in-the-cloud.

I don’t fully understand how it differs from Mathematica Online (which has no free version so I never tried it). Here’s a thread on that: Wolfram Programming Cloud vs. Mathematica Online

7

Thank you, programming cloud seems to be more Mathematica still providing much for hobby mathematics oeis.org related investigations!

wolfram.cloud.jpg
wolfram.cloud.jpg1022×410 62.6 KB

Hermann.