21497951 has 4 divisors (see below), whose sum is σ = 21710904. Its totient is φ = 21285000.

The previous prime is 21497933. The next prime is 21497953. The reversal of 21497951 is 15979412.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21497951 - 2¹⁴ = 21481567 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21497953) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 106325 + ... + 106526.

It is an arithmetic number, because the mean of its divisors is an integer number (5427726).

Almost surely, 2^21497951 is an apocalyptic number.

21497951 is a deficient number, since it is larger than the sum of its proper divisors (212953).

21497951 is a wasteful number, since it uses less digits than its factorization.

21497951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 212952.

The product of its digits is 22680, while the sum is 38.

The square root of 21497951 is about 4636.5882931311. The cubic root of 21497951 is about 278.0560546353.

The spelling of 21497951 in words is "twenty-one million, four hundred ninety-seven thousand, nine hundred fifty-one".