21721680 has 60 divisors (see below), whose sum is σ = 72951060. Its totient is φ = 5792256.

The previous prime is 21721621. The next prime is 21721717. The reversal of 21721680 is 8612712.

It can be written as a sum of positive squares in 2 ways, for example, as 10188864 + 11532816 = 3192^2 + 3396^2 .

It is a tau number, because it is divible by the number of its divisors (60).

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 14365 + ... + 15804.

It is an arithmetic number, because the mean of its divisors is an integer number (1215851).

Almost surely, 2^21721680 is an apocalyptic number.

21721680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21721680 is an abundant number, since it is smaller than the sum of its proper divisors (51229380).

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

21721680 is a wasteful number, since it uses less digits than its factorization.

21721680 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 30188 (or 30179 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21721680 is about 4660.6523148589. The cubic root of 21721680 is about 279.0173034322.

The spelling of 21721680 in words is "twenty-one million, seven hundred twenty-one thousand, six hundred eighty".