c     ------------------------------
c     prime number generator using the sieve of eratosthenes
c     converted to fortransit
c     ------------------------------
c
      dimension ifl(50)
c     *** set ending number to be tested (must match array dimension)
      isize=50
c     *** mark all numbers in the sieve as prime initially, except 2
      do 10 i=1,isize
   10   ifl(i)=1
      ifl(1)=0
c
c     *** work through the list, finding the next marked number
c
      do 40 num=1,isize
      if (ifl(num)) 15,40,15
c     *** marked number is the current prime, form its first multiple
   15 iprme=num
      mult=iprme+iprme
c     *** unmark all multiples of the current prime
   20 if (mult-isize) 25,25,40
   25 do 30 i=mult,isize,iprme
   30 ifl(i)=0
c     *** go find next unmarked number
   40 continue
c
c     *** print results - all numbers that are still marked
c
      do 50 num=1,isize
      if (ifl(num)) 45,50,45
   45 punch, num
   50 continue
      end