21557643 has 24 divisors (see below), whose sum is σ = 30728880. Its totient is φ = 13426560.

The previous prime is 21557639. The next prime is 21557651. The reversal of 21557643 is 34675512.

It is not a de Polignac number, because 21557643 - 2² = 21557639 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21557603) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 119013 + ... + 119193.

It is an arithmetic number, because the mean of its divisors is an integer number (1280370).

Almost surely, 2^21557643 is an apocalyptic number.

21557643 is a deficient number, since it is larger than the sum of its proper divisors (9171237).

21557643 is a wasteful number, since it uses less digits than its factorization.

21557643 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 287 (or 250 counting only the distinct ones).

The product of its digits is 25200, while the sum is 33.

The square root of 21557643 is about 4643.0208916179. The cubic root of 21557643 is about 278.3131703594.

The spelling of 21557643 in words is "twenty-one million, five hundred fifty-seven thousand, six hundred forty-three".