21998561 has 32 divisors (see below), whose sum is σ = 27417600. Its totient is φ = 17521920.

The previous prime is 21998539. The next prime is 21998567. The reversal of 21998561 is 16589912.

It is a happy number.

It is not a de Polignac number, because 21998561 - 2⁶ = 21998497 is a prime.

Its product of digits (38880) is a multiple of the sum of its prime divisors (80).

It is not an unprimeable number, because it can be changed into a prime (21998567) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 709616 + ... + 709646.

It is an arithmetic number, because the mean of its divisors is an integer number (856800).

Almost surely, 2^21998561 is an apocalyptic number.

It is an amenable number.

21998561 is a deficient number, since it is larger than the sum of its proper divisors (5419039).

21998561 is a wasteful number, since it uses less digits than its factorization.

21998561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 106 (or 80 counting only the distinct ones).

The product of its digits is 38880, while the sum is 41.

The square root of 21998561 is about 4690.2623593995. The cubic root of 21998561 is about 280.1978236375.

The spelling of 21998561 in words is "twenty-one million, nine hundred ninety-eight thousand, five hundred sixty-one".