20581639 has 4 divisors (see below), whose sum is σ = 22164856. Its totient is φ = 18998424.

The previous prime is 20581609. The next prime is 20581643. The reversal of 20581639 is 93618502.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 93618502 = 2 ⋅46809251.

It is a cyclic number.

It is not a de Polignac number, because 20581639 - 2⁵ = 20581607 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 (20581609) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 791589 + ... + 791614.

It is an arithmetic number, because the mean of its divisors is an integer number (5541214).

Almost surely, 2^20581639 is an apocalyptic number.

20581639 is a deficient number, since it is larger than the sum of its proper divisors (1583217).

20581639 is a wasteful number, since it uses less digits than its factorization.

20581639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1583216.

The product of its (nonzero) digits is 12960, while the sum is 34.

The square root of 20581639 is about 4536.6991304251. The cubic root of 20581639 is about 274.0480095958.

The spelling of 20581639 in words is "twenty million, five hundred eighty-one thousand, six hundred thirty-nine".