## Wednesday, March 22, 2017

### HP 15C: Prime Factorization

HP 15C: Prime Factorization

This program does exactly this: factors an integer.  Fix 0 mode is activated during execution.  Each factor is displayed by pressing [R/S].  The calculator is returned to Fix 4 mode when the program is completed.  If the integer is a prime number, the program just returns the integer entered.

 Step Key Code 001 LBL B 42, 21, 22 002 FIX 0 42, 7, 0 003 STO 2 44, 2 004 STO 0 44, 0 005 2 2 006 STO 1 44, 1 007 LBL 3 42, 21, 3 008 RCL 0 45, 0 009 RCL÷ 1 45, 10, 1 010 ENTER 36 011 FRAC 42, 44 012 X=0 43, 20 013 GTO 2 22, 2 014 1 1 015 STO+ 1 44, 40, 1 016 GTO 3 22, 3 017 LBL 2 42, 21, 2 018 RCL 1 45, 1 019 R/S 31 020 R↓ 33 021 R↓ 33 022 STO 0 44, 0 023 1 1 024 - 30 025 X≠0 43, 30, 0  (TEST 0) 026 GTO 3 22, 3 027 LBL 2 45, 2 028 FIX 4 42, 7, 4 029 RTN 43, 32

Example:  150.  Factors:  2, 3, 5, 5 (when the display reads 150.0000 the factorization ends)

This blog is property of Edward Shore, 2017.

1. Very useful factorization program for HP 15C I try it on my Samsung S7 Edge with HP 15C App.
Factorize 111,111,189 = 3*7*41*129,049 when press R/S for the last factorization it took about 7 second to get the last answer very amazing!!! consider the CPU in this smartphone. I try the same with HP Prime APP on computer it gave answer instantly using ifactor(111,111,189)
This also takes about 5 seconds for 1,177,112

Thank You for your program and keep the good work!!!

1. Update
I try Free HP PRIME APP On the S7 EDGE and the speed is lighting fast only HP 15C gave answer slower maybe because of the code build for it classic computation style.

2. HP 15C App on S7 Edge with ifactor(8,771,155) = 5*1,754,231 takes 1 minute and 12 second to compute!!!
I would like to know how long it take to compute on a real physical HP 15C LE since I don't have one.

2. We will explore the perceived random distribution of Prime Numbers. You can also download materials to know more about prime numbers.

3. This is awesome, Eddie. I have a 15c app on my android and I'm about to order the Swiss Micros DM15L.

4. Hi,
The programm can be improved by :
-Adding 2 instead of 1 after decomposing the prime number 2 (2x faster)
-Stopping just after sqrt(start_number) and not going up to star_number (2x faster which make 4x)

5. Thanks Eddie!

There seems to be an error in your program listing. Line 027 reads "LBL 2" although the keystrokes 45, 2 indicate "RCL 2". The latter would be the correct keys, right?

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