21224009 has 12 divisors (see below), whose sum is σ = 22635396. Its totient is φ = 19891872.

The previous prime is 21224003. The next prime is 21224023. The reversal of 21224009 is 90042212.

21224009 = T₁₃₄₇ + T₁₃₄₈ + ... + T₁₃₆₉.

It can be written as a sum of positive squares in 2 ways, for example, as 14227984 + 6996025 = 3772^2 + 2645^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21224009 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21224003) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 27659 + ... + 28415.

It is an arithmetic number, because the mean of its divisors is an integer number (1886283).

Almost surely, 2^21224009 is an apocalyptic number.

It is an amenable number.

21224009 is a deficient number, since it is larger than the sum of its proper divisors (1411387).

21224009 is an equidigital number, since it uses as much as digits as its factorization.

21224009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 856 (or 833 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21224009 is about 4606.9522463338. The cubic root of 21224009 is about 276.8699402894.

The spelling of 21224009 in words is "twenty-one million, two hundred twenty-four thousand, nine".