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C programming code to sum the sequence 2, 22, 222,...

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Release： 2023-09-11 10:25:02

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C programming code to sum the sequence 2, 22, 222,...

Given a sequence: 2,22,222,2222..., we need to find the sum of this sequence. Therefore, we have to find the mathematical formula for finding the sum of a series,

The explanation of the formula is like this-

sum =[2+22+222+2222&hellip;.]
sum= 2*[1+11+111+1111&hellip;.]
Sum = 2/9[9+99+999+9999&hellip;.]
sum= 2/9 [10+100+1000+10000+.....]
sum = 2/9[10+10<sup>2</sup>+10<sup>3</sup>+10<sup>4</sup>+.....]
sum=2/9*[(10<sup>n</sup>-1-9n)/9]

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Example

#include <stdio.h>
#include <math.h>
int main() {
   int n = 3;
   float sum = 2*(pow(10, n) - 1 - (9 * n))/81;
   printf("sum is %d", sum);
   return 0;
}

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Output

sum is 879

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source：tutorialspoint.com

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