江津东胜云岭翠湖出租:What number comes next in following series ? 9,12,21,48
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What number comes next in following series ? 9,12,21,48
前一项减去5,再乘以3,得到后一项
12=(9-5)×3
21=(12-5)×3
48=(21-5)×3
那么接下来就是(48-5)×3=129
前两个数差3,为3的一次方;第二个数和第三个数相差9,位3 的平方;第三个数与第四个数相差27,位3 得立方,所以我们能推断出第四个数和第五个数相差3得四次方,即81,所以48+81=129
129
a(n)=a(n-1)+3^n
129
What number comes next in following series ? 9,12,21,48
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