21817643 has 4 divisors (see below), whose sum is σ = 22965960. Its totient is φ = 20669328.

The previous prime is 21817619. The next prime is 21817693. The reversal of 21817643 is 34671812.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21817643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21817603) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 574130 + ... + 574167.

It is an arithmetic number, because the mean of its divisors is an integer number (5741490).

Almost surely, 2^21817643 is an apocalyptic number.

21817643 is a deficient number, since it is larger than the sum of its proper divisors (1148317).

21817643 is a wasteful number, since it uses less digits than its factorization.

21817643 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1148316.

The product of its digits is 8064, while the sum is 32.

The square root of 21817643 is about 4670.9359875725. The cubic root of 21817643 is about 279.4275848380.

The spelling of 21817643 in words is "twenty-one million, eight hundred seventeen thousand, six hundred forty-three".