20856605861 has 24 divisors (see below), whose sum is σ = 26014132224. Its totient is φ = 16371875520.

The previous prime is 20856605801. The next prime is 20856605893. The reversal of 20856605861 is 16850665802.

It is a happy number.

It is a de Polignac number, because none of the positive numbers 2^k-20856605861 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 (20856605801) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 80831 + ... + 219651.

It is an arithmetic number, because the mean of its divisors is an integer number (1083922176).

Almost surely, 2^20856605861 is an apocalyptic number.

It is an amenable number.

20856605861 is a deficient number, since it is larger than the sum of its proper divisors (5157526363).

20856605861 is a wasteful number, since it uses less digits than its factorization.

20856605861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 138981 (or 138968 counting only the distinct ones).

The product of its (nonzero) digits is 691200, while the sum is 47.

The spelling of 20856605861 in words is "twenty billion, eight hundred fifty-six million, six hundred five thousand, eight hundred sixty-one".