21697557 has 16 divisors (see below), whose sum is σ = 33278592. Its totient is φ = 12317760.

The previous prime is 21697531. The next prime is 21697561. The reversal of 21697557 is 75579612.

It is not a de Polignac number, because 21697557 - 2⁸ = 21697301 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21697157) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 7 + ... + 6587.

It is an arithmetic number, because the mean of its divisors is an integer number (2079912).

Almost surely, 2^21697557 is an apocalyptic number.

It is an amenable number.

21697557 is a deficient number, since it is larger than the sum of its proper divisors (11581035).

21697557 is a wasteful number, since it uses less digits than its factorization.

21697557 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6748.

The product of its digits is 132300, while the sum is 42.

The square root of 21697557 is about 4658.0636534938. The cubic root of 21697557 is about 278.9139776680.

The spelling of 21697557 in words is "twenty-one million, six hundred ninety-seven thousand, five hundred fifty-seven".