21642991 has 8 divisors (see below), whose sum is σ = 22429184. Its totient is φ = 20862360.

The previous prime is 21642979. The next prime is 21643009. The reversal of 21642991 is 19924612.

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 21642991 - 2¹³ = 21634799 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 (21642941) 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, 7540 + ... + 10006.

It is an arithmetic number, because the mean of its divisors is an integer number (2803648).

Almost surely, 2^21642991 is an apocalyptic number.

21642991 is a deficient number, since it is larger than the sum of its proper divisors (786193).

21642991 is a wasteful number, since it uses less digits than its factorization.

21642991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2781.

The product of its digits is 7776, while the sum is 34.

The square root of 21642991 is about 4652.2028115722. The cubic root of 21642991 is about 278.6799728911.

The spelling of 21642991 in words is "twenty-one million, six hundred forty-two thousand, nine hundred ninety-one".