2
$\begingroup$

$$3, 7, 12, 18, 25, \ldots$$

This sequence appears in my son's math homework. The question is to find the $n$'th term. What is the formula and how do you derive it?

  • 2
    Hint: take the difference of succeeding terms.2011-12-04
  • 4
    In principle, there are infinitely many sequences that start like this, so you cannot "derive it", the task is to find a simple recipe that gives this sequence. There is little point in looking up the recipe, but I am sure someone will provide it.2011-12-04
  • 0
    @Phira Thanks. Is there a recipe or should I just use trial-and-improvement guess work.2011-12-04
  • 4
    The answer is [42](http://en.wikipedia.org/wiki/Phrases_from_The_Hitchhiker%27s_Guide_to_the_Galaxy#The_number_42). For every $n$.2011-12-04
  • 4
    The [OEIS](http://oeis.org/search?q=3%2C7%2C12%2C18%2C25) is great for questions like these...2011-12-04
  • 1
    Pedants are NOT great for questions like these...2011-12-04

4 Answers 4