21749897 has 4 divisors (see below), whose sum is σ = 23422980. Its totient is φ = 20076816.

The previous prime is 21749891. The next prime is 21749899. The reversal of 21749897 is 79894712.

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

It can be written as a sum of positive squares in 2 ways, for example, as 5621641 + 16128256 = 2371^2 + 4016^2 .

It is a cyclic number.

It is not a de Polignac number, because 21749897 - 2¹⁴ = 21733513 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21749891) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 836522 + ... + 836547.

It is an arithmetic number, because the mean of its divisors is an integer number (5855745).

Almost surely, 2^21749897 is an apocalyptic number.

It is an amenable number.

21749897 is a deficient number, since it is larger than the sum of its proper divisors (1673083).

21749897 is a wasteful number, since it uses less digits than its factorization.

21749897 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1673082.

The product of its digits is 254016, while the sum is 47.

The square root of 21749897 is about 4663.6784837722. The cubic root of 21749897 is about 279.1380679498.

The spelling of 21749897 in words is "twenty-one million, seven hundred forty-nine thousand, eight hundred ninety-seven".