21663649 has 4 divisors (see below), whose sum is σ = 24758464. Its totient is φ = 18568836.

The previous prime is 21663647. The next prime is 21663659. The reversal of 21663649 is 94636612.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21663649 - 2¹ = 21663647 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21663647) 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, 1547397 + ... + 1547410.

It is an arithmetic number, because the mean of its divisors is an integer number (6189616).

Almost surely, 2^21663649 is an apocalyptic number.

It is an amenable number.

21663649 is a deficient number, since it is larger than the sum of its proper divisors (3094815).

21663649 is an equidigital number, since it uses as much as digits as its factorization.

21663649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3094814.

The product of its digits is 46656, while the sum is 37.

The square root of 21663649 is about 4654.4225205712. The cubic root of 21663649 is about 278.7686103657.

The spelling of 21663649 in words is "twenty-one million, six hundred sixty-three thousand, six hundred forty-nine".