21815489 has 4 divisors (see below), whose sum is σ = 22227156. Its totient is φ = 21403824.

The previous prime is 21815483. The next prime is 21815527. The reversal of 21815489 is 98451812.

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

It can be written as a sum of positive squares in 2 ways, for example, as 8456464 + 13359025 = 2908^2 + 3655^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21815489 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21815483) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 205754 + ... + 205859.

It is an arithmetic number, because the mean of its divisors is an integer number (5556789).

Almost surely, 2^21815489 is an apocalyptic number.

It is an amenable number.

21815489 is a deficient number, since it is larger than the sum of its proper divisors (411667).

21815489 is an equidigital number, since it uses as much as digits as its factorization.

21815489 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 411666.

The product of its digits is 23040, while the sum is 38.

The square root of 21815489 is about 4670.7054071093. The cubic root of 21815489 is about 279.4183888122.

The spelling of 21815489 in words is "twenty-one million, eight hundred fifteen thousand, four hundred eighty-nine".