21709691 has 2 divisors, whose sum is σ = 21709692. Its totient is φ = 21709690.

The previous prime is 21709687. The next prime is 21709693. The reversal of 21709691 is 19690712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21709691 - 2² = 21709687 is a prime.

It is a super-3 number, since 3×21709691³ (a number of 23 digits) contains 333 as substring.

Together with 21709693, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21709693) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10854845 + 10854846.

It is an arithmetic number, because the mean of its divisors is an integer number (10854846).

Almost surely, 2^21709691 is an apocalyptic number.

21709691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21709691 is an equidigital number, since it uses as much as digits as its factorization.

21709691 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6804, while the sum is 35.

The square root of 21709691 is about 4659.3659439885. The cubic root of 21709691 is about 278.9659606558.

The spelling of 21709691 in words is "twenty-one million, seven hundred nine thousand, six hundred ninety-one".