21231691 has 16 divisors (see below), whose sum is σ = 25268544. Its totient is φ = 17639424.

The previous prime is 21231677. The next prime is 21231701. The reversal of 21231691 is 19613212.

It is a cyclic number.

It is not a de Polignac number, because 21231691 - 2¹¹ = 21229643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21231601) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2995 + ... + 7171.

It is an arithmetic number, because the mean of its divisors is an integer number (1579284).

Almost surely, 2^21231691 is an apocalyptic number.

21231691 is a deficient number, since it is larger than the sum of its proper divisors (4036853).

21231691 is a wasteful number, since it uses less digits than its factorization.

21231691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4230.

The product of its digits is 648, while the sum is 25.

The square root of 21231691 is about 4607.7859108253. The cubic root of 21231691 is about 276.9033404876.

The spelling of 21231691 in words is "twenty-one million, two hundred thirty-one thousand, six hundred ninety-one".