~ 質數積概率 ~

1 - 20裡,質數有8個(2, 3, 5, 7, 11, 13, 17, 19),
2 個質數之積有6個(4, 6, 10, 14, 9, 15) ;
21 - 40裡,質數有4個(23, 29, 31, 37),
2 個質數之積有9個(22, 26, 34, 38, 21, 33, 39, 25, 35) ;
41 - 60裡,質數有5個(41, 43, 47, 53, 59),
2 個質數之積有6個(46, 58, 51, 57, 55, 49) ;
61 - 80裡,質數有4個(61, 67, 73, 79),
2 個質數之積有6個(62, 74, 69, 78, 65, 77) ;
81 - 100裡,質數有3個(83, 87, 97),
2 個質數之積有7個(82, 86, 94, 93, 85, 95, 91) ;
除了頭20個整數, 每20個整數,2 個質數之積的數目都比質數的數目多,所以,
事件一的概率比事件二的概率小

The website provide a formula about the number of almost prime.
http://en.wikipedia.org/wiki/Almost_prime

From this the density of 2 almost prime->0 and (# of prime) / (# of 2-almost prime) ->0

I am not sure if the probability is zero, but your argument is flawed because infinitely many 0 add together can become one, consider sum (i = 1 -> n) (1/n) when n tends to infinity

It seems you are asking the density/distribution of semiprimes. This has been solved. Check out the following website:
http://mathworld.wolfram.com/Semiprime.html

修改問題後仍有問題
數字是無限大的

它是質數 p 又話 = 0

依家 p1 * p2 又話 = 0

照你咁講 p1 * p2 * p3 又 0
p1 * p2 * p3 * ... p無限都 = 0

咁加埋即係 0 , 乜加埋唔係 1 咩?!

2011-11-28 18:33:05 補充：
對不起,我一時衝動語氣重咗,唔係鬧你, Sorry 啦~

是 0 嗎 ??????

2011-11-28 18:28:35 補充：
我唔講野，費時俾你鬧