21457791 has 20 divisors (see below), whose sum is σ = 33941952. Its totient is φ = 13462848.

The previous prime is 21457771. The next prime is 21457819. The reversal of 21457791 is 19775412.

It is a happy number.

It is not a de Polignac number, because 21457791 - 2⁵ = 21457759 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21457721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 6415 + ... + 9168.

Almost surely, 2^21457791 is an apocalyptic number.

21457791 is a deficient number, since it is larger than the sum of its proper divisors (12484161).

21457791 is a wasteful number, since it uses less digits than its factorization.

21457791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15612 (or 15603 counting only the distinct ones).

The product of its digits is 17640, while the sum is 36.

The square root of 21457791 is about 4632.2554981348. The cubic root of 21457791 is about 277.8828025914.

The spelling of 21457791 in words is "twenty-one million, four hundred fifty-seven thousand, seven hundred ninety-one".