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 ▼ hal Unregistered Posts: 130 Threads: 36 Joined: Jan 1970 01-31-2006, 11:28 PM I would humbly like to submit my program (written for the HP29C) to find the prime factors of a given integer, or find all primes between 2 given integers. This program could be adapted to any machine with >= 98 program lines, conditional branching, and at least 6 storage registers. Note that since the 29C doesn't have flags, I have used register 0 as a pseudo flag. Instructions: To find prime factors of an integer...put integer in x register and GSB 9. Factors are displayed successively. R/S to see the next factor. 1 is always the final factor displayed. If given integer is prime, factors displayed will be it and 1. To find primes between two integers, put lower integer into register 6, and upper integer into register 9, and GSB 8. primes will display from lowest to highest. R/S to view next prime. Display will flash one zero, then 10 zeros, then 3 zeros (fix 2) when finished.Best regards, Hal ```step# mnewmonic 1 lbl 9 2 0 set flag register to 0 for prime 3 sto 0 factors routine 4 x<>y 5 lbl 7 6 sto 04 7 sqrt 8 sto 05 set bail out point for finding factors 9 2 10 sto 1 11 gsb 1 12 3 manually check 2,3,5,7 for divisibility 13 sto 1 14 gsb 1 15 5 16 sto 1 17 gsb 1 18 7 19 sto 01 20 gsb 1 21 lbl 3 22 4 increment trial divisor by sequence 23 sto + 1 such that multiples of 2,3 and 5 24 gsb 1 are skipped 25 2 26 sto + 1 27 gsb 1 28 4 29 sto + 1 30 gsb 1 31 2 32 sto + 1 33 gsb 1 34 4 35 sto + 1 36 gsb 1 37 6 38 sto + 1 39 gsb 1 40 2 41 sto + 1 42 gsb 1 43 6 44 sto + 1 45 gsb 1 46 gto 3 47 lbl 1 48 rcl 5 49 rcl 1 50 x>y? 51 gto 5 52 rcl 04 53 x<>y 54 / 55 enter 56 frc 57 x=0? 58 gto 4 59 rtn 60 lbl 4 61 rcl 0 62 x<>0? 63 gto 2 64 rcl 1 65 r/s 66 roll dn 67 roll dn 68 roll dn 69 gto 7 70 lbl 5 71 rcl 4 72 r/s 73 rcl 0 74 x<>0? 75 gto 2 76 1 77 r/s 78 rtn 79 lbl 8 80 9 set flag register to non-zero for 81 sto 0 primes between integers routine 82 rcl 6 83 gto 7 84 lbl 2 85 1 86 sto + 6 87 rcl 9 88 rcl 6 89 x>y? 90 gto 6 91 gto 7 92 lbl 6 93 0 94 pause 95 fix 9 96 pause 97 fix 2 98 r/s ``` ▼ Trent Moseley Unregistered Posts: 406 Threads: 47 Joined: Jul 2005 02-01-2006, 02:46 PM Hi, Peter Henrici in his book "Computational Analysis with the HP-25 Pocket Calculator" has a prime program for the 25 using all 49 lines, its four storage registers, and of course no flags. tm ▼ hal Unregistered Posts: 130 Threads: 36 Joined: Jan 1970 02-01-2006, 05:38 PM I'll have to check that book out...Henrici must be a master of brevity when programming. There is a prime factors / prime numbers program for the hp67 in the software section of the this website that's 223 lines long (it has a few more bells and whistles for printing options, and error detection, etc). Best regards, Hal

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