Finds all prime numbers in a range requested and places them in a public primes() array. I've demostrated a template size of 30 (2 * 3 * 5) but larger templates can be built such 210  (2 * 3 * 5 * 7) or 2310  (2 * 3 * 5 * 7 * 11).
The larger templates are marginally faster (4 - 6%) but at great expense: 100's or 1000's of lines of code.  

The macro assigned to my "Find Primes" button is listed below:

Option Explicit

Public i As Long
Public j As Long
Public estr As Double    
Public esti As Long              ' used with estr to estimate the size of the primes array
Public iend As Long            ' user input - program will enumerate all prime <= iend
Public sr As Long                 ' square root of iend
Public PrX() As Boolean      ' Templated Possible Primes
Public Primes() As Long      ' # Primes <= iend

Sub DefinePrimes()

With ThisWorkbook.Worksheets("Sheet1")   ' rename the sheet if needed
  iend = .Cells(1, 5)
  If iend < 40 Then
    iend = 40
  End If
 
  estr = 1 / (WorksheetFunction.Ln(iend) - 1.15)
  esti = Int(estr * iend)
ReDim PrX(iend + 30)           ' we always want to have a little extra space
ReDim Primes(esti)               ' we always want to have a little extra space
  sr = Sqr(iend)
  .Cells(1, 4) = "Find Primes <= "
  .Cells(1, 5) = iend
  .Cells(2, 4) = "estr ="
  .Cells(2, 5) = estr
  .Cells(3, 4) = "esti ="
  .Cells(3, 5) = esti
  .Cells(4, 4) = "sr ="
  .Cells(4, 5) = sr
  PrX(2) = True
  PrX(3) = True
 …

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