21691799 has 4 divisors (see below), whose sum is σ = 21742560. Its totient is φ = 21641040.

The previous prime is 21691793. The next prime is 21691843. The reversal of 21691799 is 99719612.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21691799 - 2⁸ = 21691543 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 (21691793) 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, 24734 + ... + 25595.

It is an arithmetic number, because the mean of its divisors is an integer number (5435640).

Almost surely, 2^21691799 is an apocalyptic number.

21691799 is a deficient number, since it is larger than the sum of its proper divisors (50761).

21691799 is an equidigital number, since it uses as much as digits as its factorization.

21691799 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50760.

The product of its digits is 61236, while the sum is 44.

The square root of 21691799 is about 4657.4455445018. The cubic root of 21691799 is about 278.8893031733.

The spelling of 21691799 in words is "twenty-one million, six hundred ninety-one thousand, seven hundred ninety-nine".