21891457 has 8 divisors (see below), whose sum is σ = 25695296. Its totient is φ = 18256752.

The previous prime is 21891449. The next prime is 21891473. The reversal of 21891457 is 75419812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21891457 - 2³ = 21891449 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21891437) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 42003 + ... + 42520.

It is an arithmetic number, because the mean of its divisors is an integer number (3211912).

Almost surely, 2^21891457 is an apocalyptic number.

It is an amenable number.

21891457 is a deficient number, since it is larger than the sum of its proper divisors (3803839).

21891457 is an equidigital number, since it uses as much as digits as its factorization.

21891457 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 84567.

The product of its digits is 20160, while the sum is 37.

The square root of 21891457 is about 4678.8307300008. The cubic root of 21891457 is about 279.7423522786.

The spelling of 21891457 in words is "twenty-one million, eight hundred ninety-one thousand, four hundred fifty-seven".