Pascal’s Triangle Generator (Build 1–20 Rows)

Quick start

• Choose “Rows” (1–20). Row 1 is 1, row 2 is 1 1, etc.
• Click Generate to render the triangle as a table.
• Use Copy Result to copy a tab-separated version (easy to paste into spreadsheets or code).

What is Pascal’s Triangle?

Pascal’s Triangle is an infinite triangular array of integers built from a simple rule: every row starts and ends with 1, and each interior value equals the sum of the two values directly above it. Although it is commonly associated with Blaise Pascal (17th century), versions of the triangle appeared much earlier in several mathematical traditions.

The triangle is more than a curiosity: it is a compact “index” of binomial coefficients (combinations), and it also reveals patterns connected to algebra (binomial expansion), probability (binomial distribution), and number theory (divisibility and modular patterns).

How the triangle is constructed (rule)

If we count rows starting at 0 (top row is row 0), the value in row n and position k (starting at 0) is traditionally written as:

with boundary values:

• Edges: P(n, 0) = 1 and P(n, n) = 1
• Interior: computed by adding the two numbers above

This generator uses that exact addition rule, building each row from the row before it.

Connection to binomial coefficients (combinations)

Every entry in Pascal’s Triangle is a binomial coefficient:

Interpretation: (n choose k) counts how many ways to choose k items from n items without order.

When using this page, remember the UI asks for a number of rows starting from the top. If you generate R rows, you are producing rows n = 0 through n = R − 1 in the 0-based binomial-coefficient convention.

How to interpret the output

• Row meaning: Row 1 in the display (the first generated row) is 1, which corresponds to n = 0.
• Symmetry: Each row reads the same left-to-right and right-to-left because (n choose k) = (n choose n − k).
• Row sums: The sum of values in row n is 2^n. This matches the fact that an n-element set has 2^n subsets.
• Where to find a coefficient: In row n, the k-th entry (starting at 0) equals (n choose k).

Worked example (Rows = 5)

If you enter Rows = 5, the generator outputs 5 rows:

1
1 1
1 2 1
1 3 3 1
1 4 6 4 1

These correspond to n = 0..4. Now connect this to the binomial theorem. The coefficients in the expansion of (a + b)^4 are:

(a + b)^4 = 1·a^4 + 4·a^3b + 6·a^2b^2 + 4·ab^3 + 1·b^4

Those coefficients (1, 4, 6, 4, 1) match the last generated row above. In general, the coefficients of (a + b)^n are the numbers in row n of Pascal’s Triangle (with the top row as n = 0).

Common patterns you can spot quickly

Pascal’s Triangle contains many well-known patterns. Here are a few that are easy to verify with small row counts:

• Ones on the edges: every row begins and ends with 1.
• Counting numbers: the second diagonal is 1, 2, 3, 4, … (these are (n choose 1)).
• Triangular numbers: the third diagonal is 1, 3, 6, 10, 15, … (these are (n choose 2)).
• Fibonacci numbers: summing shallow diagonals produces 1, 1, 2, 3, 5, 8, ….
• Modular patterns: coloring entries by odd/even produces a Sierpiński-triangle-like fractal pattern.

Pascal’s Triangle vs. “nCr” calculators

Limitations & assumptions

• Row limit (1–20): The tool caps output at 20 rows for readability and performance, especially on mobile.
• Row indexing: The first generated row is 1 (equivalent to n = 0 in (n choose k) notation). Generating R rows produces coefficients up to n = R − 1.
• Integer-only: This generator is for standard integer rows and does not compute generalized binomial coefficients (e.g., fractional or negative exponents).
• Number size: Up to 20 rows, values remain within JavaScript’s safe integer range. Much larger rows can exceed Number.MAX_SAFE_INTEGER and require BigInt/other handling.
• Formatting: The “Copy Result” format is tab-separated values (TSV) with one row per line; it’s designed for pasting into spreadsheets and plain-text editors.

Related calculators

If you want to compute a single coefficient or use these values in probability, you may also like a combinations (nCr) tool and a binomial distribution calculator.