SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/tech-big-o-ignores-constants

In Big O notation, what do you ignore when describing an algorithm's running time?

Constant factors and low-order terms, so 3n² + 5n + 7 is just O(n²).

Start playing free

  1. The size of the input
  2. The highest power of n
  3. Constant factors and low-order terms ✔

Why: Big O describes how time grows as the input gets huge. At large n, the biggest term wins, and a fixed multiplier like 3 matters far less than whether growth is n or n squared.

Huh, didn't know that: An O(n) algorithm with a big constant can lose to an O(n²) one on tiny inputs, which is why real libraries sometimes switch methods for small lists.

The dad joke
Big O walked into a bar and ordered 3n squared plus 5n drinks. The bartender just poured n squared.
Like this card?
Play the game

References

Answer: Constant factors and low-order terms. Big O describes how time grows as the input gets huge. At large n, the biggest term wins, and a fixed multiplier like 3 matters far less than whether growth is n or n squared.

  1. MIT 6.006 Introduction to Algorithms, Lecture 1: Introduction ocw.mit.edu/courses/6-006-introduction-to-algorithms-spring-2020/resources/mit6_006s20_lec1
    Asymptotic Notation: ignore constant factors and low order terms
    Checked 2026-10-10.

Think this answer is wrong? Tap "Challenge this answer" on the card in the game and tell us why.

Test yourself in the game

Tech & GadgetsHow fast is binary search on a sorted array of n items, in Big O terms?Tech & GadgetsWhat must be true about a list before you can use binary search on it?Tech & GadgetsWhat is the worst-case running time of insertion sort on n items?

That's stuff everyone should know.