;+ ; NAME: ; FACPRIME ; ; PURPOSE: ; Factor a number into its prime numbers. ; ; CATEGORY: ; Math. ; ; CALLING SEQUENCE: ; ; Result = FACPRIME( N, SUM=Sum ) ; ; INPUTS: ; N: Number to factor into primes. ; ; OUTPUTS: ; Returns a two dimensional array, LONARR(2,nprime) where nprime ; is the number of unique prime numbers. The first dimension holds ; the value of each unique prime, Result(0,*) and the second ; dimension holds the frequency or number of times that prime ; occurs, Result(1,*). ; ; COMMON BLOCKS: ; FACPRIME: Holds an array containing the first 100000 prime numbers. ; ; RESTRICTIONS: ; The number to be factored must be < 1299709. ; ; EXAMPLE: ; ; pnums = FACPRIME( 63500 ) ; Factor 63500 into it pnums ; help, pnums ; pnums LONG = Array(2,3) ; print,REFORM(pnums(0,*) ; 2 5 127 ; print,REFORM(pnums(1,*) ; 2 3 1 ; ck = 1L ; (2^2)(5^3)(127) = 63500 ; for i=0,2 do \$ ; ck=ck*long(pnums(0,i))^pnums(1,*) ; ; MODIFICATION HISTORY: ; Written by: Han Wen, August 1996. ; 11-Aug-1996 Missing prime number, 2 in factoring, eliminate ; prime number, 1 from result. ;- function FACPRIME, N1, SUM=Sum common FACPRIME, prime_num if (N_ELEMENTS(prime_num) eq 0) then \$ restore,GRPKPATH()+'prime10.sav' N = N1 i = 0L r = [1L,0L] repeat begin r = [r,prime_num(i),0] repeat begin rem = N mod prime_num(i) if (rem eq 0) then begin N = N/prime_num(i) j = 2L*(i+2)-1 r(j) = r(j) + 1 endif endrep until (rem ne 0) i = i+1L endrep until (N lt prime_num(i)) r = REFORM(r,2,i+1,/OVERWRITE) hgt0 = WHERE(r(1,*) gt 0) r = r(*,hgt0) sum = LONG(TOTAL(REFORM(r(0,*))*REFORM(r(1,*)))) return,r end