21057991680 has 176 divisors, whose sum is σ = 73476229824. Its totient is φ = 5104926720.

The previous prime is 21057991657. The next prime is 21057991687. The reversal of 21057991680 is 8619975012.

It is a tau number, because it is divible by the number of its divisors (176).

It is a Harshad number since it is a multiple of its sum of digits (48).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21057991687) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 106644 + ... + 231276.

Almost surely, 2^21057991680 is an apocalyptic number.

21057991680 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 21057991680, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36738114912).

21057991680 is an abundant number, since it is smaller than the sum of its proper divisors (52418238144).

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

21057991680 is a wasteful number, since it uses less digits than its factorization.

21057991680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 124672 (or 124654 counting only the distinct ones).

The product of its (nonzero) digits is 272160, while the sum is 48.

The spelling of 21057991680 in words is "twenty-one billion, fifty-seven million, nine hundred ninety-one thousand, six hundred eighty".