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:

197 students sent a solution.
5 points:	144 students.
4 points:	30 students.
3 points:	7 students.
2 points:	5 students.
1 point:	6 students.
0 point:	5 students.

Problems in Mathematics of KöMaL, October 2014