21509872 has 20 divisors (see below), whose sum is σ = 41845536. Its totient is φ = 10711040.

The previous prime is 21509867. The next prime is 21509897. The reversal of 21509872 is 27890512.

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 3 ways as a sum of consecutive naturals, for example, 1497 + ... + 6727.

Almost surely, 2^21509872 is an apocalyptic number.

It is an amenable number.

21509872 is a deficient number, since it is larger than the sum of its proper divisors (20335664).

21509872 is a wasteful number, since it uses less digits than its factorization.

21509872 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5496 (or 5490 counting only the distinct ones).

The product of its (nonzero) digits is 10080, while the sum is 34.

The square root of 21509872 is about 4637.8736507154. The cubic root of 21509872 is about 278.1074408306.

The spelling of 21509872 in words is "twenty-one million, five hundred nine thousand, eight hundred seventy-two".