20851215840 has 576 divisors, whose sum is σ = 89734200192. Its totient is φ = 4290969600.

The previous prime is 20851215817. The next prime is 20851215841. The reversal of 20851215840 is 4851215802.

20851215840 is a `hidden beast` number, since 2 + 0 + 8 + 51 + 21 + 584 + 0 = 666.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 20851215795 and 20851215804.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20851215841) 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 95 ways as a sum of consecutive naturals, for example, 5370700 + ... + 5374580.

It is an arithmetic number, because the mean of its divisors is an integer number (155788542).

Almost surely, 2^20851215840 is an apocalyptic number.

20851215840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 20851215840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44867100096).

20851215840 is an abundant number, since it is smaller than the sum of its proper divisors (68882984352).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

20851215840 is a wasteful number, since it uses less digits than its factorization.

20851215840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3963 (or 3952 counting only the distinct ones).

The product of its (nonzero) digits is 25600, while the sum is 36.

The spelling of 20851215840 in words is "twenty billion, eight hundred fifty-one million, two hundred fifteen thousand, eight hundred forty".