21021020538 has 128 divisors (see below), whose sum is σ = 52399872000. Its totient is φ = 5487989760.

The previous prime is 21021020513. The next prime is 21021020539. The reversal of 21021020538 is 83502012012.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21021020539) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 2908293 + ... + 2915511.

It is an arithmetic number, because the mean of its divisors is an integer number (409374000).

Almost surely, 2^21021020538 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21021020538, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26199936000).

21021020538 is an abundant number, since it is smaller than the sum of its proper divisors (31378851462).

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

21021020538 is a wasteful number, since it uses less digits than its factorization.

21021020538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7380.

The product of its (nonzero) digits is 960, while the sum is 24.

The spelling of 21021020538 in words is "twenty-one billion, twenty-one million, twenty thousand, five hundred thirty-eight".