1. [1] Abramowitz, M. and Stegun, I. A. (1970). Handbook of Mathematical Functions. National Bureau of Standards, Washington.
2. [2] Rehman, A., Mubeen, S., Ahmad, M. O. and Siddiqi, S. R. (2017). - Multiple Factorials with Applications. Punjab University Journal of Mathematics, (ISSN 1016-2526), Vol. 49(2) pp. 1-11.
3. [3] Mubeen, S. and Rehman, A. (2014). -Factorials. Journal of Inequalities and Special Functions, 5. No.3, pp. 14-20.
4. [4] Mubeen, S., Rehman, G. and Arshad, M. (2015). K-Gamma, K-Beta Matrix Functions and their Properties. J. Math. Comp. Sci., No. 5, pp. 647-657, ISSN:1927-5307.
5. [5] Thukral, A. K. (2014). Factorials of Real Negative and Imaginary Numbers – A New Perspective. Springer plus. 3:658 doi : 101186/2193-1801-3-658.