Prime Numbers?

[Keith]

Hello,
I am looking for a function that will return a prime
number in Excel. Is there such a thing? Is it possible
to obtain prime numbers in a simple and easy way?

Keith

 

[Frank Kabel]

Hi Keith
=3
<vbg>
but I don't thinks this is what you want. what are you trying to
achieve (generating prime numbers within a range, getting the largest
prime within a range, sieving primes, etc?). You may have a look at
http://www.utm.edu/research/primes/

Frank

 

[Bob Phillips]

Keith,

Here is a routine originally presented by Myrna Larson that I use to test
for primes.

=IsPrime(num)

returns True or False.

Function IsPrime(TestNum As Long)
Dim PrimeCnt As Long
Dim y As Long
Dim x As Long
Dim i As Long
Dim Flag As Boolean
Dim Primes() As Long
Dim NumStop As Double
ReDim Primes(1 To 2)

NumStop = Sqr(TestNum)
If TestNum = 1 Or TestNum = 2 Or TestNum = 3 Or TestNum = 5 Then
IsPrime = True
Exit Function
End If
Primes(1) = 2
Primes(2) = 3
PrimeCnt = 2
x = 3

Do
x = x + 2
For y = 3 To Sqr(x) Step 2
If x Mod y = 0 Then GoTo NoPrime1
Next y
PrimeCnt = PrimeCnt + 1
ReDim Preserve Primes(1 To PrimeCnt)
Primes(PrimeCnt) = x
NoPrime1:
Loop Until Primes(PrimeCnt) > NumStop

For i = LBound(Primes) To UBound(Primes)
If TestNum Mod Primes(i) = 0 Then
IsPrime = False
Exit Function
End If
Next
IsPrime = True
End Function

--

HTH

Bob Phillips
... looking out across Poole Harbour to the Purbecks
(remove nothere from the email address if mailing direct)

 

[Niek Otten]

Hi Keith,

If you do a search on Internet you will find lists of prime numbers and
agorithms to create such a list.
What exactly do you require? Just one prome numer or a function that takes a
prime number randomly from a list?

--

Kind Regards,

Niek Otten

Microsoft MVP - Excel

 

[Keith Willshaw]

Hello,
I am looking for a function that will return a prime
number in Excel. Is there such a thing? Is it possible
to obtain prime numbers in a simple and easy way?

Keith

see the code at the bottom of this page

http://members.chello.nl/n.sterk/ExcelPages/Files/excel_files.htm


Keith Willshaw

 

[Keith]

Thank you to all who replied.
I actually am attempting to generate a list of primes, so
the routine that tests for primes will work, and I'll also
look at the other suggestions.

thanks very much,

keith

 

[Frank Kabel]

Thank you to all who replied.
I actually am attempting to generate a list of primes, so
the routine that tests for primes will work, and I'll also
look at the other suggestions.

thanks very much,

keith

Hi Keith
I would suggest to import an existing list of primes. e.g.
http://www.utm.edu/research/primes/lists/small/1000.txt

Frank

 

[ds]

Here's another new suggestion:

I do not quite know if this software can contribute,
but i just wanted to let you know, that we developed a collection
of functions (library, dll) for working with real big numbers.
(...numbers bigger than the normal data types a programmer can handle.)

It was made for Visual Basic, but can be used in
any language that can invoke a .DLL (such as C++, VBA in Excel, Access or
whatever)

It's the only DLL available for Windows for UNLIMITED BIG NUMBERS
with functions such as: +/-* Power2, Power10, MOD DIVIDE, ISPRIME, COMPARE,
Xor etc...

Calculations are sometimes even faster than you are used to, cause
everything was made in assembly. It's shareware and it is online on
http://www.big-numbers.com

David

 

[Nia]

Where can I get the function
=IsPrime(num

I typed it in a cell and got an error message
Is there an add-on for more functions in Excel

I want an IF test for a cel
=IF(IsPrime(B1),"Prime","Composite")

 

[Bob Phillips]

Hi Nia,

Here is a routine originally presented by Myrna Larson that I use to test
for primes.

=IsPrime(num)

returns True or False.

Function IsPrime(TestNum As Long)
Dim PrimeCnt As Long
Dim y As Long
Dim x As Long
Dim i As Long
Dim Flag As Boolean
Dim Primes() As Long
Dim NumStop As Double
ReDim Primes(1 To 2)

NumStop = Sqr(TestNum)
If TestNum = 1 Or TestNum = 2 Or TestNum = 3 Or TestNum = 5 Then
IsPrime = True
Exit Function
End If
Primes(1) = 2
Primes(2) = 3
PrimeCnt = 2
x = 3

Do
x = x + 2
For y = 3 To Sqr(x) Step 2
If x Mod y = 0 Then GoTo NoPrime1
Next y
PrimeCnt = PrimeCnt + 1
ReDim Preserve Primes(1 To PrimeCnt)
Primes(PrimeCnt) = x
NoPrime1:
Loop Until Primes(PrimeCnt) > NumStop

For i = LBound(Primes) To UBound(Primes)
If TestNum Mod Primes(i) = 0 Then
IsPrime = False
Exit Function
End If
Next
IsPrime = True
End Function


--

HTH

Bob Phillips
... looking out across Poole Harbour to the Purbecks
(remove nothere from the email address if mailing direct)