Meserve, B. E.«Classroom Notes: Double Factorials».The American Mathematical Monthly,55,7,1948,p.425–426. DOI: 10.2307/2306136.
Mezey, Paul G.«Some dimension problems in molecular databases».Journal of Mathematical Chemistry,45,1,2009,p.1–6. DOI: 10.1007/s10910-008-9365-8.
Dale, M. R. T.;Moon, J. W.«The permuted analogues of three Catalan sets».Journal of Statistical Planning and Inference,34,1,1993,p.75–87. DOI: 10.1016/0378-3758(93)90035-5.
O'Connor, John J.;Robertson, Edmund F.«Abu Ali al-Hasan ibn al-Haytham»(en anglès).MacTutor History of Mathematics archive. School of Mathematics and Statistics, University of St Andrews, Scotland.