21682991 has 4 divisors (see below), whose sum is σ = 23654184. Its totient is φ = 19711800.

The previous prime is 21682987. The next prime is 21683017. The reversal of 21682991 is 19928612.

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 21682991 - 2² = 21682987 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 (21682901) 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, 985580 + ... + 985601.

It is an arithmetic number, because the mean of its divisors is an integer number (5913546).

Almost surely, 2^21682991 is an apocalyptic number.

21682991 is a deficient number, since it is larger than the sum of its proper divisors (1971193).

21682991 is a wasteful number, since it uses less digits than its factorization.

21682991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1971192.

The product of its digits is 15552, while the sum is 38.

The square root of 21682991 is about 4656.4998657790. The cubic root of 21682991 is about 278.8515502028.

The spelling of 21682991 in words is "twenty-one million, six hundred eighty-two thousand, nine hundred ninety-one".