(9n+1)^3同餘1(mod 9)
(9n+2)^3同餘-1(mod 9)
(9n+3)^3同餘0(mod 9)
(9n+4)^3同餘1(mod 9)
(9n+5)^3同餘-1(mod 9)
(9n+6)^3同餘0(mod 9)
(9n+7)^3同餘1(mod 9)
(9n+8)^3同餘-1(mod 9)
由上可知 三個立方數相加時 無法出現被九除餘四或五的數
#ed_op#br#ed_cl#對,5也是一個反例...#ed_op#br#ed_cl#5=( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl#+( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl#+( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl##ed_op#br#ed_cl#??is 寫到:#ed_op#div#ed_cl#那麼#ed_op#/div#ed_cl##ed_op#div#ed_cl#4=( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl#+( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl#+( )#ed_op#sup#ed_cl#3#ed_op#/sup#ed_cl##ed_op#/div#ed_cl##ed_op#div#ed_cl##ed_op#sup#ed_cl#我怎麼都想不到...#ed_op#img src="/phpBB2/richedit/smileys/aa104.gif"#ed_cl##ed_op#/sup#ed_cl##ed_op#/div#ed_cl#
#ed_op#br#ed_cl#該是任何#ed_op#span style="font-weight: bold;"#ed_cl#正#ed_op#/span#ed_cl#整數嗎?有必要大於2嗎?#ed_op#br#ed_cl#4=1+1+2,而2不是立方數吧~~#ed_op#br#ed_cl##ed_op#br#ed_cl##ed_op#br#ed_cl#tangpakchiu 寫到:#ed_op#div#ed_cl#試證或反證任何一個整數都可表示成三個立方數之和。#ed_op#/div#ed_cl##ed_op#div#ed_cl##ed_op#/div#ed_cl#