21208921680 has 40 divisors (see below), whose sum is σ = 65747657952. Its totient is φ = 5655712384.

The previous prime is 21208921673. The next prime is 21208921681. The reversal of 21208921680 is 8612980212.

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21208921681) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 44185014 + ... + 44185493.

Almost surely, 2^21208921680 is an apocalyptic number.

21208921680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21208921680 is an abundant number, since it is smaller than the sum of its proper divisors (44538736272).

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

21208921680 is a wasteful number, since it uses less digits than its factorization.

21208921680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 88370523 (or 88370517 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 39.

The spelling of 21208921680 in words is "twenty-one billion, two hundred eight million, nine hundred twenty-one thousand, six hundred eighty".