'*********************************************
'*              PRIME NUMBERS                *
'* ----------------------------------------- *
'* This small program tests if a given inte- *
'* ger number is a prime number or not.      *
'* ----------------------------------------- *
'* Ref.: "Mathematiques par l'informatique   *
'*        individuelle (1) par H. Lehning    *
'*        et D. Jakubowicz, Masson, Paris,   *
'*        1982" [BIBLI 06].                  *
'*********************************************
'See also program factors.bas
cls
print
input " ? ", N
print
'Test if multiple of 2
D=N-2*INT(N/2)
if D=0 then goto 100
'Test if multiple of 3
D=N-3*INT(N/3)
if D=0 then goto 100
'Test if multiple of 6i-1 and 6i+1 from i=6 to sqr(N)+1
For I%=6 to INT(SQR(N))+1 step 6
  D=N-(I%-1)*INT(N/(I%-1))
  if D=0 then goto 100
  D=N-(I%+1)*INT(N/(I%+1))
  if D=0 then goto 100
Next I%
print " Prime number.":end
100 print " Not a prime number."
end

'end of file prime.bas