21709997 has 4 divisors (see below), whose sum is σ = 21721920. Its totient is φ = 21698076.

The previous prime is 21709967. The next prime is 21710011. The reversal of 21709997 is 79990712.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21709997 - 2¹⁶ = 21644461 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21709927) 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, 2597 + ... + 7082.

It is an arithmetic number, because the mean of its divisors is an integer number (5430480).

Almost surely, 2^21709997 is an apocalyptic number.

It is an amenable number.

21709997 is a deficient number, since it is larger than the sum of its proper divisors (11923).

21709997 is an equidigital number, since it uses as much as digits as its factorization.

21709997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11922.

The product of its (nonzero) digits is 71442, while the sum is 44.

The square root of 21709997 is about 4659.3987809588. The cubic root of 21709997 is about 278.9672713329.

It can be divided in two parts, 2170 and 9997, that added together give a cube (12167 = 23³).

The spelling of 21709997 in words is "twenty-one million, seven hundred nine thousand, nine hundred ninety-seven".