21209649 has 4 divisors (see below), whose sum is σ = 28279536. Its totient is φ = 14139764.

The previous prime is 21209633. The next prime is 21209653. The reversal of 21209649 is 94690212.

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 21209649 - 2⁴ = 21209633 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21209609) 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, 3534939 + ... + 3534944.

It is an arithmetic number, because the mean of its divisors is an integer number (7069884).

Almost surely, 2^21209649 is an apocalyptic number.

It is an amenable number.

21209649 is a deficient number, since it is larger than the sum of its proper divisors (7069887).

21209649 is an equidigital number, since it uses as much as digits as its factorization.

21209649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7069886.

The product of its (nonzero) digits is 7776, while the sum is 33.

The square root of 21209649 is about 4605.3934685323. The cubic root of 21209649 is about 276.8074835161.

The spelling of 21209649 in words is "twenty-one million, two hundred nine thousand, six hundred forty-nine".