20305991 has 4 divisors (see below), whose sum is σ = 20321184. Its totient is φ = 20290800.

The previous prime is 20305981. The next prime is 20306017. The reversal of 20305991 is 19950302.

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 20305991 - 2¹⁸ = 20043847 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 (20305921) 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, 5375 + ... + 8336.

It is an arithmetic number, because the mean of its divisors is an integer number (5080296).

Almost surely, 2^20305991 is an apocalyptic number.

20305991 is a deficient number, since it is larger than the sum of its proper divisors (15193).

20305991 is a wasteful number, since it uses less digits than its factorization.

20305991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15192.

The product of its (nonzero) digits is 2430, while the sum is 29.

The square root of 20305991 is about 4506.2169277566. The cubic root of 20305991 is about 272.8190735439.

The spelling of 20305991 in words is "twenty million, three hundred five thousand, nine hundred ninety-one".