21971691 has 12 divisors (see below), whose sum is σ = 36270832. Its totient is φ = 12555216.

The previous prime is 21971687. The next prime is 21971707. The reversal of 21971691 is 19617912.

It is not a de Polignac number, because 21971691 - 2² = 21971687 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21971681) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 174316 + ... + 174441.

Almost surely, 2^21971691 is an apocalyptic number.

21971691 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21971691 is a deficient number, since it is larger than the sum of its proper divisors (14299141).

21971691 is a wasteful number, since it uses less digits than its factorization.

21971691 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 348770 (or 348767 counting only the distinct ones).

The product of its digits is 6804, while the sum is 36.

The square root of 21971691 is about 4687.3970388692. The cubic root of 21971691 is about 280.0836952181.

The spelling of 21971691 in words is "twenty-one million, nine hundred seventy-one thousand, six hundred ninety-one".