21213990 has 96 divisors (see below), whose sum is σ = 63737856. Its totient is φ = 4795200.

The previous prime is 21213971. The next prime is 21213991. The reversal of 21213990 is 9931212.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21213991) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 95019 + ... + 95241.

It is an arithmetic number, because the mean of its divisors is an integer number (663936).

Almost surely, 2^21213990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21213990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31868928).

21213990 is an abundant number, since it is smaller than the sum of its proper divisors (42523866).

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

21213990 is a wasteful number, since it uses less digits than its factorization.

21213990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 394 (or 391 counting only the distinct ones).

The product of its (nonzero) digits is 972, while the sum is 27.

The square root of 21213990 is about 4605.8647396553. The cubic root of 21213990 is about 276.8263670490.

The spelling of 21213990 in words is "twenty-one million, two hundred thirteen thousand, nine hundred ninety".