20856439906 has 4 divisors (see below), whose sum is σ = 31284659862. Its totient is φ = 10428219952.

The previous prime is 20856439889. The next prime is 20856439909. The reversal of 20856439906 is 60993465802.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 20853959281 + 2480625 = 144409^2 + 1575^2 .

It is not an unprimeable number, because it can be changed into a prime (20856439909) 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 as a sum of consecutive naturals, namely, 5214109975 + ... + 5214109978.

Almost surely, 2^20856439906 is an apocalyptic number.

20856439906 is a deficient number, since it is larger than the sum of its proper divisors (10428219956).

20856439906 is a wasteful number, since it uses less digits than its factorization.

20856439906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10428219955.

The product of its (nonzero) digits is 2799360, while the sum is 52.

The spelling of 20856439906 in words is "twenty billion, eight hundred fifty-six million, four hundred thirty-nine thousand, nine hundred six".