# On quadratic sequences | Mark Ritchings

This is a guest post from Mark Ritchings, a maths tutor in Bury.

A quadratic sequence is a sequence for which the $n$th term is $an^2+bn+c$. The constants $b$ and/or $c$ might be zero but $a$ definitely isn’t.
The first term is $a\times 1^2 +b \times 1 + c = a+b+c$.
The second term is $a \times 2^2 +b \times 2 + c = 4a+2b+c$.
The third term is $a \times 3^2+b\times 3+c=9a+3b+c$.

… so, if you know the values of $a$, $b$ and $c$ you can work any term of the sequence.

In their wisdom, the people who decide what mathematics you have to learn and what you will be tested on have decided…