21091842720 has 480 divisors, whose sum is σ = 83663217792. Its totient is φ = 4965193728.

The previous prime is 21091842719. The next prime is 21091842757. The reversal of 21091842720 is 2724819012.

21091842720 is a `hidden beast` number, since 210 + 9 + 18 + 427 + 2 + 0 = 666.

It is a tau number, because it is divible by the number of its divisors (480).

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

It is an unprimeable number.

It is a polite number, since it can be written in 79 ways as a sum of consecutive naturals, for example, 3872319 + ... + 3877761.

Almost surely, 2^21091842720 is an apocalyptic number.

21091842720 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 21091842720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41831608896).

21091842720 is an abundant number, since it is smaller than the sum of its proper divisors (62571375072).

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

21091842720 is a wasteful number, since it uses less digits than its factorization.

21091842720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5506 (or 5489 counting only the distinct ones).

The product of its (nonzero) digits is 16128, while the sum is 36.

The spelling of 21091842720 in words is "twenty-one billion, ninety-one million, eight hundred forty-two thousand, seven hundred twenty".