21506851872 has 144 divisors (see below), whose sum is σ = 66867589152. Its totient is φ = 6502824960.

The previous prime is 21506851859. The next prime is 21506851973. The reversal of 21506851872 is 27815860512.

21506851872 is a `hidden beast` number, since 2 + 1 + 5 + 0 + 68 + 518 + 72 = 666.

It is a tau number, because it is divible by the number of its divisors (144).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1472188 + ... + 1486724.

It is an arithmetic number, because the mean of its divisors is an integer number (464358258).

Almost surely, 2^21506851872 is an apocalyptic number.

21506851872 is a gapful number since it is divisible by the number (22) 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 21506851872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33433794576).

21506851872 is an abundant number, since it is smaller than the sum of its proper divisors (45360737280).

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

21506851872 is a wasteful number, since it uses less digits than its factorization.

21506851872 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 15031 (or 15020 counting only the distinct ones).

The product of its (nonzero) digits is 268800, while the sum is 45.

It can be divided in two parts, 21506 and 851872, that added together give a palindrome (873378).

The spelling of 21506851872 in words is "twenty-one billion, five hundred six million, eight hundred fifty-one thousand, eight hundred seventy-two".