Re: How many natural numbers less than 10^8 are there, whose sum of digits equals 7?

Posted by XIPP on Dec 03, 2013; 3:03am
URL: http://discussion-forum.276.s1.nabble.com/How-many-natural-numbers-less-than-10-8-are-there-whose-sum-of-digits-equals-7-tp7584287p7584291.html

Many many thanks, Aditya. Will you please let me know where did you learn this technique? Also, will you recommend some book for combinatorics?