21557397 has 8 divisors (see below), whose sum is σ = 29012256. Its totient is φ = 14237072.

The previous prime is 21557387. The next prime is 21557401. The reversal of 21557397 is 79375512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21557397 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21557387) 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 7 ways as a sum of consecutive naturals, for example, 33258 + ... + 33899.

It is an arithmetic number, because the mean of its divisors is an integer number (3626532).

Almost surely, 2^21557397 is an apocalyptic number.

It is an amenable number.

21557397 is a deficient number, since it is larger than the sum of its proper divisors (7454859).

21557397 is a wasteful number, since it uses less digits than its factorization.

21557397 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 67267.

The product of its digits is 66150, while the sum is 39.

The square root of 21557397 is about 4642.9944001689. The cubic root of 21557397 is about 278.3121117202.

The spelling of 21557397 in words is "twenty-one million, five hundred fifty-seven thousand, three hundred ninety-seven".