21243649 has 16 divisors (see below), whose sum is σ = 25231360. Its totient is φ = 17502480.

The previous prime is 21243637. The next prime is 21243683. The reversal of 21243649 is 94634212.

It is a happy number.

It is a cyclic number.

It is not a de Polignac number, because 21243649 - 2⁹ = 21243137 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (31).

It is a self number, because there is not a number n which added to its sum of digits gives 21243649.

It is not an unprimeable number, because it can be changed into a prime (21243049) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 48172 + ... + 48610.

It is an arithmetic number, because the mean of its divisors is an integer number (1576960).

Almost surely, 2^21243649 is an apocalyptic number.

It is an amenable number.

21243649 is a deficient number, since it is larger than the sum of its proper divisors (3987711).

21243649 is a wasteful number, since it uses less digits than its factorization.

21243649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 700.

The product of its digits is 10368, while the sum is 31.

The square root of 21243649 is about 4609.0833144997. The cubic root of 21243649 is about 276.9553160729.

The spelling of 21243649 in words is "twenty-one million, two hundred forty-three thousand, six hundred forty-nine".