21746991 has 8 divisors (see below), whose sum is σ = 33138304. Its totient is φ = 12426840.

The previous prime is 21746981. The next prime is 21746999. The reversal of 21746991 is 19964712.

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

It is not a de Polignac number, because 21746991 - 2¹⁰ = 21745967 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 (21746999) 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, 517765 + ... + 517806.

It is an arithmetic number, because the mean of its divisors is an integer number (4142288).

Almost surely, 2^21746991 is an apocalyptic number.

21746991 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21746991 is a deficient number, since it is larger than the sum of its proper divisors (11391313).

21746991 is a wasteful number, since it uses less digits than its factorization.

21746991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1035581.

The product of its digits is 27216, while the sum is 39.

The square root of 21746991 is about 4663.3669167244. The cubic root of 21746991 is about 279.1256355330.

The spelling of 21746991 in words is "twenty-one million, seven hundred forty-six thousand, nine hundred ninety-one".