21721288 has 8 divisors (see below), whose sum is σ = 40727430. Its totient is φ = 10860640.

The previous prime is 21721279. The next prime is 21721303. The reversal of 21721288 is 88212712.

It can be written as a sum of positive squares in only one way, i.e., 20593444 + 1127844 = 4538^2 + 1062^2 .

It is a tau number, because it is divible by the number of its divisors (8).

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 as a sum of consecutive naturals, namely, 1357573 + ... + 1357588.

Almost surely, 2^21721288 is an apocalyptic number.

It is an amenable number.

21721288 is a deficient number, since it is larger than the sum of its proper divisors (19006142).

21721288 is a wasteful number, since it uses less digits than its factorization.

21721288 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2715167 (or 2715163 counting only the distinct ones).

The product of its digits is 3584, while the sum is 31.

The square root of 21721288 is about 4660.6102604702. The cubic root of 21721288 is about 279.0156249948.

The spelling of 21721288 in words is "twenty-one million, seven hundred twenty-one thousand, two hundred eighty-eight".