21249409 has 4 divisors (see below), whose sum is σ = 21334320. Its totient is φ = 21164500.

The previous prime is 21249331. The next prime is 21249443. The reversal of 21249409 is 90494212.

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 21249409 - 2⁷ = 21249281 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21246409) 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, 42079 + ... + 42580.

It is an arithmetic number, because the mean of its divisors is an integer number (5333580).

Almost surely, 2^21249409 is an apocalyptic number.

It is an amenable number.

21249409 is a deficient number, since it is larger than the sum of its proper divisors (84911).

21249409 is an equidigital number, since it uses as much as digits as its factorization.

21249409 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 84910.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 21249409 is about 4609.7081252504. The cubic root of 21249409 is about 276.9803450194.

The spelling of 21249409 in words is "twenty-one million, two hundred forty-nine thousand, four hundred nine".