## Saturday, January 29, 2005

### Finding Primes Using The Number 3

Away back when in one of my blogs I was advancing the theory that this universe is based on the number 3. For instance, we have 3 dimensions, length, width and height. Three strikes and you’re out. Things, good or bad, usually happen in 3’s. Most discussions have 3 major points. Traffic lights usually have 3 lights, red for stop, yellow for caution and green for go. You are usually given 3 chances to accomplish something. Most people can only remember 3 things on a list. The triangle, consisting of 3 sides is the strongest form of construction. The people you know in your life can be classified as acquaintances, friends and soulmates. If you organize a speech, tell them what you are going to say, say it and tell them what you said. Anyway, I got to thinking about primes again. Prime numbers are numbers that you can only divided evenly by themselves and one. For instance 17 is a prime number. It can only be divided evenly by itself and 1. If you divide 17 by any number that precedes it the answer is a fraction (Ex: 17/4 = 4 ¼ ). If you look at a table of prime numbers you will see their last digit is a 1, 3, 7 or 9 once you get beyond 1 digit numbers such as 5 or 2.

Finding Primes Using The Number 3

A prime number usually ends in 1, 3, 7 or 9.
Total the digits in the number ending in 1, 3, 7 or 9 (ex. 677 has the digits (6,7,7,) when totaled = 20 (6 +7 +7 = 20)
Divide the digit total (20) by 3,
If the answer contains a fraction (20/3 = 6.666666667) 677 is a prime.
If the answer doesn’t contain a fraction the number is not a prime. For instance 27 isn’t a prime because (2+7=9) and 9 divided by 3 is an even number ( 9/3 =3.)

Prime =11
Total = 2
Total / 3 = 0.666666667
Prime =13
Total = 4
Total / 3 = 1.333333333
Prime =17
Total = 8
Total/3= 2.666666667
Prime = 19
Total = 10
Total /3 = 3.333333333
Prime = 23
Total = 5
Total/3 = 1.666666667
Prime = 29
Total = 11
Total/3= 3.666666667
Prime = 31
Total = 4
Total/3 = 1.333333333
Prime = 37
Total = 10
Total / 3 = 3.333333333
Prime = 41
Total = 5
Total/3 = 1.666666667
Prime =43
Total = 7
Total/3 = 2.333333333
Prime= 47
Total = 11
Total/3 = 3.666666667