21756009 has 16 divisors (see below), whose sum is σ = 31728384. Its totient is φ = 13150800.

The previous prime is 21755959. The next prime is 21756041. The reversal of 21756009 is 90065712.

It is not a de Polignac number, because 21756009 - 2⁹ = 21755497 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21752009) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 17994 + ... + 19164.

It is an arithmetic number, because the mean of its divisors is an integer number (1983024).

Almost surely, 2^21756009 is an apocalyptic number.

It is an amenable number.

21756009 is a deficient number, since it is larger than the sum of its proper divisors (9972375).

21756009 is a wasteful number, since it uses less digits than its factorization.

21756009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1748.

The product of its (nonzero) digits is 3780, while the sum is 30.

The square root of 21756009 is about 4664.3337144763. Note that the first 3 decimals coincide. The cubic root of 21756009 is about 279.1642126266.

The spelling of 21756009 in words is "twenty-one million, seven hundred fifty-six thousand, nine".