21998565 has 24 divisors (see below), whose sum is σ = 38252760. Its totient is φ = 11695104.

The previous prime is 21998539. The next prime is 21998567. The reversal of 21998565 is 56589912.

21998565 is nontrivially palindromic in base 2.

It can be written as a sum of positive squares in 4 ways, for example, as 459684 + 21538881 = 678^2 + 4641^2 .

It is not a de Polignac number, because 21998565 - 2⁸ = 21998309 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a self number, because there is not a number n which added to its sum of digits gives 21998565.

It is a congruent number.

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 23 ways as a sum of consecutive naturals, for example, 18921 + ... + 20049.

It is an arithmetic number, because the mean of its divisors is an integer number (1593865).

Almost surely, 2^21998565 is an apocalyptic number.

It is an amenable number.

21998565 is a deficient number, since it is larger than the sum of its proper divisors (16254195).

21998565 is a wasteful number, since it uses less digits than its factorization.

21998565 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1573 (or 1570 counting only the distinct ones).

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

The square root of 21998565 is about 4690.2627858149. The cubic root of 21998565 is about 280.1978406203.

It can be divided in two parts, 219 and 98565, that multiplied together give a triangular number (21585735 = T₆₅₇₀).

The spelling of 21998565 in words is "twenty-one million, nine hundred ninety-eight thousand, five hundred sixty-five".