21181890 has 64 divisors (see below), whose sum is σ = 53343360. Its totient is φ = 5376000.

The previous prime is 21181889. The next prime is 21181891. The reversal of 21181890 is 9818112.

It is an interprime number because it is at equal distance from previous prime (21181889) and next prime (21181891).

It is a super-3 number, since 3×21181890³ (a number of 23 digits) contains 333 as substring.

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

It is not an unprimeable number, because it can be changed into a prime (21181891) 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, 84265 + ... + 84515.

It is an arithmetic number, because the mean of its divisors is an integer number (833490).

Almost surely, 2^21181890 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21181890, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26671680).

21181890 is an abundant number, since it is smaller than the sum of its proper divisors (32161470).

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

21181890 is a wasteful number, since it uses less digits than its factorization.

21181890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 387.

The product of its (nonzero) digits is 1152, while the sum is 30.

The square root of 21181890 is about 4602.3787327859. The cubic root of 21181890 is about 276.6866697365.

The spelling of 21181890 in words is "twenty-one million, one hundred eighty-one thousand, eight hundred ninety".