21731009 has 4 divisors (see below), whose sum is σ = 21766080. Its totient is φ = 21695940.

The previous prime is 21730991. The next prime is 21731029. The reversal of 21731009 is 90013712.

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 21731009 - 2¹⁶ = 21665473 is a prime.

It is a super-3 number, since 3×21731009³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21731029) 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, 16589 + ... + 17850.

It is an arithmetic number, because the mean of its divisors is an integer number (5441520).

Almost surely, 2^21731009 is an apocalyptic number.

It is an amenable number.

21731009 is a deficient number, since it is larger than the sum of its proper divisors (35071).

21731009 is an equidigital number, since it uses as much as digits as its factorization.

21731009 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 35070.

The product of its (nonzero) digits is 378, while the sum is 23.

The square root of 21731009 is about 4661.6530329916. The cubic root of 21731009 is about 279.0572417162.

The spelling of 21731009 in words is "twenty-one million, seven hundred thirty-one thousand, nine".