20668391 has 4 divisors (see below), whose sum is σ = 21108192. Its totient is φ = 20228592.

The previous prime is 20668367. The next prime is 20668397. The reversal of 20668391 is 19386602.

20668391 = 640² + 641² + ... + 686².

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19386602 = 2 ⋅9693301.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20668391 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 (20668397) 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, 219830 + ... + 219923.

It is an arithmetic number, because the mean of its divisors is an integer number (5277048).

Almost surely, 2^20668391 is an apocalyptic number.

20668391 is a deficient number, since it is larger than the sum of its proper divisors (439801).

20668391 is an equidigital number, since it uses as much as digits as its factorization.

20668391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 439800.

The product of its (nonzero) digits is 15552, while the sum is 35.

The square root of 20668391 is about 4546.2502130877. The cubic root of 20668391 is about 274.4325090682.

The spelling of 20668391 in words is "twenty million, six hundred sixty-eight thousand, three hundred ninety-one".