My lovely Math

That was really funny :D
It's been a math lesson today and a new theme was 'Sequences', just the basics. And when we had a practice we had to write a general term expression... so, there was an example we couldn't find a general term, the difference between the neighbour terms was = 1, 2, 3, 5, 8, 13, 21, 34, 55, 89... We were sitting in the silence waiting for the teacher's help but he just said "Guys, I don't remember the answer :D". And then my groupmate behind me just said "Isn't it Fibonacci sequence?.." Gosh, it was this.
Why the first-year economist have to deduce such an awful formulae? *broken brain*