21799991 has 8 divisors (see below), whose sum is σ = 22214784. Its totient is φ = 21387960.

The previous prime is 21799979. The next prime is 21800003. The reversal of 21799991 is 19999712.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21799979) and next prime (21800003).

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 21799991 - 2¹⁰ = 21798967 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 (21799901) 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, 21686 + ... + 22668.

It is an arithmetic number, because the mean of its divisors is an integer number (2776848).

Almost surely, 2^21799991 is an apocalyptic number.

21799991 is a deficient number, since it is larger than the sum of its proper divisors (414793).

21799991 is an equidigital number, since it uses as much as digits as its factorization.

21799991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1381.

The product of its digits is 91854, while the sum is 47.

The square root of 21799991 is about 4669.0460481773. The cubic root of 21799991 is about 279.3522056818.

The spelling of 21799991 in words is "twenty-one million, seven hundred ninety-nine thousand, nine hundred ninety-one".