20668591 has 4 divisors (see below), whose sum is σ = 20708784. Its totient is φ = 20628400.

The previous prime is 20668589. The next prime is 20668631. The reversal of 20668591 is 19586602.

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 20668591 - 2¹ = 20668589 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 20668591.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20668511) 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, 19315 + ... + 20356.

It is an arithmetic number, because the mean of its divisors is an integer number (5177196).

Almost surely, 2^20668591 is an apocalyptic number.

20668591 is a deficient number, since it is larger than the sum of its proper divisors (40193).

20668591 is an equidigital number, since it uses as much as digits as its factorization.

20668591 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40192.

The product of its (nonzero) digits is 25920, while the sum is 37.

The square root of 20668591 is about 4546.2722091841. The cubic root of 20668591 is about 274.4333942576.

The spelling of 20668591 in words is "twenty million, six hundred sixty-eight thousand, five hundred ninety-one".