21021138 has 12 divisors (see below), whose sum is σ = 45545838. Its totient is φ = 7007040.

The previous prime is 21021127. The next prime is 21021157. The reversal of 21021138 is 83112012.

It can be written as a sum of positive squares in only one way, i.e., 11675889 + 9345249 = 3417^2 + 3057^2 .

It is a Harshad number since it is a multiple of its sum of digits (18), and also a Moran number because the ratio is a prime number: 1167841 = 21021138 / (2 + 1 + 0 + 2 + 1 + 1 + 3 + 8).

It is a self number, because there is not a number n which added to its sum of digits gives 21021138.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 583903 + ... + 583938.

Almost surely, 2^21021138 is an apocalyptic number.

21021138 is an abundant number, since it is smaller than the sum of its proper divisors (24524700).

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

21021138 is a wasteful number, since it uses less digits than its factorization.

21021138 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1167849 (or 1167846 counting only the distinct ones).

The product of its (nonzero) digits is 96, while the sum is 18.

The square root of 21021138 is about 4584.8814597544. The cubic root of 21021138 is about 275.9849550715.

It can be divided in two parts, 2102 and 1138, that added together give a triangular number (3240 = T₈₀).

The spelling of 21021138 in words is "twenty-one million, twenty-one thousand, one hundred thirty-eight".