Prime Factorisation & Primality Checker
Check whether a whole number is prime and break it into prime factors in exponent form, with exact BigInt arithmetic for very large numbers.
Runs on your device
Result
Results appear here as you type.
What it does
Enter any whole number. Factors are found by trial division with a 6k ± 1 wheel, which is instant for numbers whose second largest prime factor is below about ten billion.
How to use it
- Enter a whole number of 2 or more.
- Read the factorisation and number of divisors.
- Use it for GCD, LCM or simplification work.
Example
360 = 2³ × 3² × 5, with 24 divisors. Select Try an example above to see it.
When it helps
- Number theory homework.
- Simplifying radicals and fractions.
- Checking RSA toy examples.
Questions
Is 1 prime?
No. A prime has exactly two distinct divisors, and 1 has only one.
How large can the number be?
Up to 30 digits. Factorisation stops with a message if a very large prime factor makes it too slow.
More student & maths tools
See all 12- Fraction Calculator Add, subtract, multiply and divide fractions, mixed numbers and decimals, with results simplified to lowest terms and shown as mixed numbers.
- Definite Integral Calculator (Numerical) Numerically evaluate a definite integral of f(x) between two limits using Simpson’s rule, with the formula, step size and a trapezoidal cross check.
- Permutation & Combination Calculator Calculate nPr and nCr (combinations) exactly for large n using BigInt, plus factorials, with the formulas and substituted values shown.
- Scientific Expression Calculator Evaluate expressions such as 2sin(30) + sqrt(16)/3 with trig, logs, powers and factorials, in degrees or radians, without using eval.
- Quadratic Equation Solver Solve ax² + bx + c = 0 with full working: the formula, substituted values, discriminant and real or complex roots, step by step.
- Percentage Calculator Work out X% of Y, what percent one number is of another, percentage increase or decrease, and add or subtract a percentage, with the working shown.
People also use
Browse all 200 tools- Contact List CSV Cleaner Clean a contacts CSV: remove duplicate emails, trim spaces, fix name capitalisation and drop invalid addresses, with spreadsheet safe output. Leads & site analysis
- Remove Solid Background (Make Transparent) Turn a white, green screen or other solid colour background transparent and download a PNG. Ideal for logos, signatures and product shots. Media & files
- SQL Formatter Beautify messy SQL queries with consistent indentation and keyword case for MySQL, PostgreSQL, SQL Server, SQLite and more. Developer
- Google SERP Snippet Preview Preview how a title and meta description may be truncated in Google desktop results, using an approximate pixel width model rather than plain character counts. SEO