21171990 has 64 divisors (see below), whose sum is σ = 59512320. Its totient is φ = 4719360.

The previous prime is 21171989. The next prime is 21171991. The reversal of 21171990 is 9917112.

It is an interprime number because it is at equal distance from previous prime (21171989) and next prime (21171991).

It is a Harshad number since it is a multiple of its sum of digits (30).

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21171991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 7381 + ... + 9839.

It is an arithmetic number, because the mean of its divisors is an integer number (929880).

Almost surely, 2^21171990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21171990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29756160).

21171990 is an abundant number, since it is smaller than the sum of its proper divisors (38340330).

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

21171990 is a wasteful number, since it uses less digits than its factorization.

21171990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2517.

The product of its (nonzero) digits is 1134, while the sum is 30.

The square root of 21171990 is about 4601.3030763035. The cubic root of 21171990 is about 276.6435570446.

The spelling of 21171990 in words is "twenty-one million, one hundred seventy-one thousand, nine hundred ninety".