21001056 has 24 divisors (see below), whose sum is σ = 55128024. Its totient is φ = 7000320.

The previous prime is 21001049. The next prime is 21001081. The reversal of 21001056 is 65010012.

It is a tau number, because it is divible by the number of its divisors (24).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 109285 + ... + 109476.

It is an arithmetic number, because the mean of its divisors is an integer number (2297001).

Almost surely, 2^21001056 is an apocalyptic number.

It is an amenable number.

21001056 is an abundant number, since it is smaller than the sum of its proper divisors (34126968).

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

21001056 is a wasteful number, since it uses less digits than its factorization.

21001056 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 218774 (or 218766 counting only the distinct ones).

The product of its (nonzero) digits is 60, while the sum is 15.

The square root of 21001056 is about 4582.6909125535. The cubic root of 21001056 is about 275.8970420430.

Adding to 21001056 its reverse (65010012), we get a palindrome (86011068).

The spelling of 21001056 in words is "twenty-one million, one thousand, fifty-six".