1. Department of Mathematics, Graphic Era Hill University, Dehradun 248002, Uttarakhand, India
2. Government Inter College, Purwaladogi, Tehri (Garhwal) 249192, Uttarakhand, India
3. Department of Mathematics, H. N. B. Garhwal University, Campus Pauri (Garhwal) 246001, Uttarakhand, India