21809791 has 8 divisors (see below), whose sum is σ = 22117824. Its totient is φ = 21504000.

The previous prime is 21809789. The next prime is 21809863. The reversal of 21809791 is 19790812.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21809791 - 2¹ = 21809789 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21809791.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21809741) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 28666 + ... + 29416.

It is an arithmetic number, because the mean of its divisors is an integer number (2764728).

Almost surely, 2^21809791 is an apocalyptic number.

21809791 is a deficient number, since it is larger than the sum of its proper divisors (308033).

21809791 is a wasteful number, since it uses less digits than its factorization.

21809791 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1121.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21809791 is about 4670.0953951713. The cubic root of 21809791 is about 279.3940595445.

The spelling of 21809791 in words is "twenty-one million, eight hundred nine thousand, seven hundred ninety-one".