C program to find Decagonal Number
A decagonal number is a figurate number that extends the concept of triangular and square numbers to the decagon (a ten-sided polygon). The nth decagonal numbers counts the number of dots in a pattern of n nested decagons, all sharing a common corner, where the ith decagon in the pattern has sides made of i dots spaced one unit apart from each other. The n-th decagonal number is given by the formula D(n)=4n2-3n; The first few decagonal numbers are: 0, 1, 10, 27, 52, 85, 126, 175, 232, 297, 370, 451, 540, 637, 742, 855, 976, 1105, 1242…… Examples:
Input : n = 2
Output : 10
Input : n = 5
Output : 85
Input : n = 7
Output: 175
CPP
#include <stdio.h>
#include <stdlib.h>
int decagonalNum( int n)
{
return (4 * n * n - 3 * n);
}
int main()
{
int n = 10;
printf ("Decagonal Number is = %d",
decagonalNum(n));
return 0;
}
|
Output:
Decagonal Number is = 370
Time complexity: O(1) as constant operations are done
Auxiliary space: O(1)
References : Mathworld
Last Updated :
19 Sep, 2022
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