21250009 has 4 divisors (see below), whose sum is σ = 23181840. Its totient is φ = 19318180.

The previous prime is 21250007. The next prime is 21250039. The reversal of 21250009 is 90005212.

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 21250009 - 2¹ = 21250007 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21250001) 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, 965899 + ... + 965920.

It is an arithmetic number, because the mean of its divisors is an integer number (5795460).

Almost surely, 2^21250009 is an apocalyptic number.

It is an amenable number.

21250009 is a deficient number, since it is larger than the sum of its proper divisors (1931831).

21250009 is a wasteful number, since it uses less digits than its factorization.

21250009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1931830.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 21250009 is about 4609.7732048334. The cubic root of 21250009 is about 276.9829519412.

The spelling of 21250009 in words is "twenty-one million, two hundred fifty thousand, nine".