21021390 has 128 divisors (see below), whose sum is σ = 62052480. Its totient is φ = 5031936.

The previous prime is 21021389. The next prime is 21021419. The reversal of 21021390 is 9312012.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 185974 + ... + 186086.

It is an arithmetic number, because the mean of its divisors is an integer number (484785).

Almost surely, 2^21021390 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21021390, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31026240).

21021390 is an abundant number, since it is smaller than the sum of its proper divisors (41031090).

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

21021390 is a wasteful number, since it uses less digits than its factorization.

21021390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 195 (or 189 counting only the distinct ones).

The product of its (nonzero) digits is 108, while the sum is 18.

The square root of 21021390 is about 4584.9089412986. The cubic root of 21021390 is about 275.9860578969.

The spelling of 21021390 in words is "twenty-one million, twenty-one thousand, three hundred ninety".