http://bg.wikipedia.org/wiki/%D0%92%...86%D0%B8%D1%8F
http://www.math10.com/forumbg/files/ae___126.gif
http://www.math10.com/forumbg/viewtopic.php?t=6311
http://bg.wikipedia.org/wiki/%D0%9A%...86.D0.B8.D0.B8
http://elearning-phys.uni-sofia.bg/~vgi/Lect4.pdf
http://stancho.roncho.net/HighMath3/Prob/Comb/Comb.html

Само това намерих и мисля, че ще ти е достатъчно.