1、n+n是偶數(shù),n+n+1是奇數(shù).
（1）當(dāng)n是偶數(shù),n+1是奇數(shù).如：n=2,4,6.,n+n=偶數(shù)+偶數(shù)=偶數(shù),n+n+1=偶數(shù)+奇數(shù)=奇數(shù)
（2）當(dāng)n是奇數(shù),n+1是偶數(shù).如：n=1,3,5.,n+n=奇數(shù)+奇數(shù)=偶數(shù),n+n+1=奇數(shù)+偶數(shù)=奇數(shù)
2、若n表示正整數(shù),則2n偶數(shù),2n+1是奇數(shù),2n-1是奇數(shù)
（1）當(dāng)n是偶數(shù),n+1是奇數(shù),n-1是奇數(shù).如：n=2,4,6.,2n=n+n=偶數(shù)+偶數(shù)=偶數(shù),2n+1=n+n+1=偶數(shù)+奇數(shù)=奇數(shù),2n-1=n+n-1=偶數(shù)+奇數(shù)=奇數(shù)
（2）當(dāng)n是奇數(shù),n+1是偶數(shù),n-1是偶數(shù).如：n=1,3,5.,2n=n+n=奇數(shù)+奇數(shù)=偶數(shù),2n+1=n+n+1=奇數(shù)+偶數(shù)=奇數(shù),2n-1=n+n-1=奇數(shù)+偶數(shù)=奇數(shù)