PREVPRIME

This function finds the greatest prime that is strictly less than the given integer.

For an integer n, it returns a prime p such that p < n and there is no prime q with p < q < n.

This operation is useful when traversing prime values in descending order.

Excel Usage

=PREVPRIME(n)

• n (int, required): Upper bound integer.

Returns (int): Largest prime number strictly less than n.

Example 1: Previous prime below ten

Inputs:

n
10

Excel formula:

=PREVPRIME(10)

Expected output:

7

Example 2: Previous prime below thirteen

Inputs:

n
13

Excel formula:

=PREVPRIME(13)

Expected output:

11

Example 3: Previous prime below one hundred

Inputs:

n
100

Excel formula:

=PREVPRIME(100)

Expected output:

97

Example 4: Previous prime below three

Inputs:

n
3

Excel formula:

=PREVPRIME(3)

Expected output:

2

Python Code

from sympy import prevprime as sympy_prevprime

def prevprime(n):
    """
    Return the largest prime smaller than a given integer.

    See: https://docs.sympy.org/latest/modules/ntheory.html

    This example function is provided as-is without any representation of accuracy.

    Args:
        n (int): Upper bound integer.

    Returns:
        int: Largest prime number strictly less than n.
    """
    try:
        result = sympy_prevprime(n)
        return int(result)
    except Exception as e:
        return f"Error: {str(e)}"

Online Calculator

n *

Upper bound integer.