21645703872 has 420 divisors, whose sum is σ = 71811343296. Its totient is φ = 6437283840.

The previous prime is 21645703861. The next prime is 21645703889. The reversal of 21645703872 is 27830754612.

21645703872 is a `hidden beast` number, since 2 + 1 + 6 + 4 + 570 + 3 + 8 + 72 = 666.

It is a super-2 number, since 2×21645703872² (a number of 21 digits) contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 59 ways as a sum of consecutive naturals, for example, 27158578 + ... + 27159374.

Almost surely, 2^21645703872 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21645703872, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35905671648).

21645703872 is an abundant number, since it is smaller than the sum of its proper divisors (50165639424).

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

21645703872 is a wasteful number, since it uses less digits than its factorization.

21645703872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 878 (or 846 counting only the distinct ones).

The product of its (nonzero) digits is 564480, while the sum is 45.

The spelling of 21645703872 in words is "twenty-one billion, six hundred forty-five million, seven hundred three thousand, eight hundred seventy-two".