20391691 has 4 divisors (see below), whose sum is σ = 20414800. Its totient is φ = 20368584.

The previous prime is 20391677. The next prime is 20391713. The reversal of 20391691 is 19619302.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19619302 = 2 ⋅9809651.

It is a cyclic number.

It is not a de Polignac number, because 20391691 - 2¹¹ = 20389643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (20391661) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10176 + ... + 12013.

It is an arithmetic number, because the mean of its divisors is an integer number (5103700).

Almost surely, 2^20391691 is an apocalyptic number.

20391691 is a deficient number, since it is larger than the sum of its proper divisors (23109).

20391691 is an equidigital number, since it uses as much as digits as its factorization.

20391691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23108.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 20391691 is about 4515.7160008132. The cubic root of 20391691 is about 273.2023394063.

The spelling of 20391691 in words is "twenty million, three hundred ninety-one thousand, six hundred ninety-one".