21565998 has 24 divisors (see below), whose sum is σ = 46851168. Its totient is φ = 7169472.

The previous prime is 21565993. The next prime is 21566003. The reversal of 21565998 is 89956512.

21565998 is a `hidden beast` number, since 2 + 1 + 56 + 599 + 8 = 666.

It is an interprime number because it is at equal distance from previous prime (21565993) and next prime (21566003).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21565993) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6411 + ... + 9177.

It is an arithmetic number, because the mean of its divisors is an integer number (1952132).

Almost surely, 2^21565998 is an apocalyptic number.

21565998 is an abundant number, since it is smaller than the sum of its proper divisors (25285170).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21565998 is a wasteful number, since it uses less digits than its factorization.

21565998 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3208 (or 3205 counting only the distinct ones).

The product of its digits is 194400, while the sum is 45.

The square root of 21565998 is about 4643.9205419559. The cubic root of 21565998 is about 278.3491205821.

The spelling of 21565998 in words is "twenty-one million, five hundred sixty-five thousand, nine hundred ninety-eight".