21635989 has 4 divisors (see below), whose sum is σ = 21879180. Its totient is φ = 21392800.

The previous prime is 21635983. The next prime is 21636007. The reversal of 21635989 is 98953612.

It is a happy number.

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 9090225 + 12545764 = 3015^2 + 3542^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21635989 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21635983) by changing a digit.

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, 121462 + ... + 121639.

It is an arithmetic number, because the mean of its divisors is an integer number (5469795).

Almost surely, 2^21635989 is an apocalyptic number.

It is an amenable number.

21635989 is a deficient number, since it is larger than the sum of its proper divisors (243191).

21635989 is an equidigital number, since it uses as much as digits as its factorization.

21635989 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 243190.

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

The square root of 21635989 is about 4651.4502039687. The cubic root of 21635989 is about 278.6499165457.

The spelling of 21635989 in words is "twenty-one million, six hundred thirty-five thousand, nine hundred eighty-nine".