21681598 has 4 divisors (see below), whose sum is σ = 32522400. Its totient is φ = 10840798.

The previous prime is 21681553. The next prime is 21681599. The reversal of 21681598 is 89518612.

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

It is a Smith number, since the sum of its digits (40) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a self number, because there is not a number n which added to its sum of digits gives 21681598.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681599) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5420398 + ... + 5420401.

It is an arithmetic number, because the mean of its divisors is an integer number (8130600).

Almost surely, 2^21681598 is an apocalyptic number.

21681598 is a deficient number, since it is larger than the sum of its proper divisors (10840802).

21681598 is a wasteful number, since it uses less digits than its factorization.

21681598 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10840801.

The product of its digits is 34560, while the sum is 40.

The square root of 21681598 is about 4656.3502875106. The cubic root of 21681598 is about 278.8455785708.

The spelling of 21681598 in words is "twenty-one million, six hundred eighty-one thousand, five hundred ninety-eight".