Problem C. 1245. (October 2014)
C. 1245. Consider two consecutive triangular numbers and add one of them to the triple of the other. Prove that the result is also a triangular number.
(5 pont)
Deadline expired on November 10, 2014.
Statistics:
198 students sent a solution.  
5 points:  145 students. 
4 points:  30 students. 
3 points:  7 students. 
2 points:  5 students. 
1 point:  6 students. 
0 point:  5 students. 
