Driver Code
int main ( ) { long int n = 6 ; cout << n << " th ▁ centered " << " ▁ octagonal ▁ number ▁ : ▁ " ; cout << cen_octagonalnum ( n ) ; cout << endl ; n = 11 ; cout << n << " th ▁ centered " << " ▁ octagonal ▁ number ▁ : ▁ " ; cout << cen_octagonalnum ( n ) ; return 0 ; }