21006872 has 8 divisors (see below), whose sum is σ = 39387900. Its totient is φ = 10503432.

The previous prime is 21006863. The next prime is 21006877. The reversal of 21006872 is 27860012.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21006877) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1312922 + ... + 1312937.

Almost surely, 2^21006872 is an apocalyptic number.

It is an amenable number.

21006872 is a deficient number, since it is larger than the sum of its proper divisors (18381028).

21006872 is a wasteful number, since it uses less digits than its factorization.

21006872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2625865 (or 2625861 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 21006872 is about 4583.3254302962. The cubic root of 21006872 is about 275.9225085258.

Adding to 21006872 its reverse (27860012), we get a palindrome (48866884).

The spelling of 21006872 in words is "twenty-one million, six thousand, eight hundred seventy-two".