20597991 has 4 divisors (see below), whose sum is σ = 27463992. Its totient is φ = 13731992.

The previous prime is 20597971. The next prime is 20598001. The reversal of 20597991 is 19979502.

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 20597991 - 2¹³ = 20589799 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20597971) 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, 3432996 + ... + 3433001.

It is an arithmetic number, because the mean of its divisors is an integer number (6865998).

Almost surely, 2^20597991 is an apocalyptic number.

20597991 is a deficient number, since it is larger than the sum of its proper divisors (6866001).

20597991 is an equidigital number, since it uses as much as digits as its factorization.

20597991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6866000.

The product of its (nonzero) digits is 51030, while the sum is 42.

The square root of 20597991 is about 4538.5009639748. The cubic root of 20597991 is about 274.1205669337.

The spelling of 20597991 in words is "twenty million, five hundred ninety-seven thousand, nine hundred ninety-one".