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Wheel Factorization





ALGORITHM

# Find the first few prime numbers. This can be done quickly using Sieve Of Eratosthenes .
# Multiply the prime numbers together to give the result ''n''.
# Write 1 to ''n'' in a circle. This will be the inner-most circle.
# Taking ''x'' to be the number of circles written so far, continue to write ''xn'' + 1 to (''x'' + 1)''n'' in another circle around the inner-most circle, such that ''xn'' + 1 is in the same position as (''x'' − 1)''n''7 + 1.
# Repeat steps 4 and 5 until the largest number to be tested for primality.
# Strike off the number 1.
# Strike off the spokes of prime numbers (found in step 1) with its multiples without striking off the numbers in the inner-most circles.
# Strike off the spokes of all multiples of prime numbers found in step 1.
# The remaining numbers in the wheel contain mostly prime numbers. Use other methods such as Sieve of Eratosthenes to remove the remaining non-primes.


EXAMPLE

1. Found the first 2 prime numbers--2 and 3.

2. ''n'' = 2 · 3 = 6

3.
1 2 3 4 5 6

4. ''x'' = 1. ''xn'' + 1 = 1 · 6 + 1 = 7. (''x'' + 1)''n'' = (1 + 1) · 6 = 12. Write 7 to 12 with 7 aligned with 1.
1 2 3 4 5 6
7 8 9 10 11 12
5. ''x'' = 2. ''xn'' + 1 = 2 · 6 + 1 = 13. (''x'' + 1)''n'' = (2 + 1) · 6 = 18. Write 13 to 18. Repeat for the next few lines.
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30
6. Sieving
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30
7. Sieving
1 2 3 4 5 6
7 8 9 10 11 12
13 14 15 16 17 18
19 20 21 22 23 24
25 26 27 28 29 30
8. Resultant list contain a non-prime 25. Use other methods of sieve to arrive at
2 3 5 7 11 13 17 19 23 29


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