(12C+) how many primes between two numbers

[Don Shepherd]

Here is a cute little program for the 12c+ that will tell you the number of prime numbers between two numbers you specify. It takes a rather brute force approach, which is why I recommend it for the 12c+ and not the slower 12c.

It also uses the N financial register as a flag. If you set N=0, it will just tell you the number of primes between the two numbers you specify. If you set N to anything else, it will pause and show you (briefly) each prime that it finds, and give you the total primes at the end. I think this is a neat and easy way to use N as a flag.

To use the program, set N to 0 or non-zero depending upon whether you want to see each prime, then enter your range in X and Y (lower point in Y, upper point in X), then press R/S and be amazed. It works best if your range is under 1000 or 2000, because although the 12c+ is fast, it is still brute force.

Code:


01 sto 2
02 x<->y
03 sto 1
04 0
05 sto 3
06 rcl 1
07 2
08 /
09 frac
10 x=0
11 goto 13
12 goto 15
13 1
14 sto+1
15 3
16 sto 0
17 rcl 1
18 sqrt
19 sto 6
20 rcl 1
21 rcl 0
22 /
23 frac
24 x=0
25 goto 39
26 2
27 sto+0
28 rcl 6
29 rcl 0
30 x<=y
31 goto 20
32 rcl n
33 x=0
34 goto 37
35 rcl 1
36 pse
37 1
38 sto+3
39 2
40 sto+1
41 rcl 2
42 rcl 1
43 x<=y
44 goto 15
45 rcl 3