21563998 has 8 divisors (see below), whose sum is σ = 32755680. Its totient is φ = 10645440.

The previous prime is 21563959. The next prime is 21564001. The reversal of 21563998 is 89936512.

It is a happy number.

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

It is a congruent number.

It is an unprimeable number.

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 3 ways as a sum of consecutive naturals, for example, 68083 + ... + 68398.

It is an arithmetic number, because the mean of its divisors is an integer number (4094460).

Almost surely, 2^21563998 is an apocalyptic number.

21563998 is a deficient number, since it is larger than the sum of its proper divisors (11191682).

21563998 is a wasteful number, since it uses less digits than its factorization.

21563998 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 136562.

The product of its digits is 116640, while the sum is 43.

The square root of 21563998 is about 4643.7052016682. The cubic root of 21563998 is about 278.3405157489.

The spelling of 21563998 in words is "twenty-one million, five hundred sixty-three thousand, nine hundred ninety-eight".