21081018 has 64 divisors (see below), whose sum is σ = 50964480. Its totient is φ = 5683392.

The previous prime is 21081017. The next prime is 21081019. The reversal of 21081018 is 81018012.

It is an interprime number because it is at equal distance from previous prime (21081017) and next prime (21081019).

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a junction number, because it is equal to n+sod(n) for n = 21080985 and 21081003.

It is not an unprimeable number, because it can be changed into a prime (21081017) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 134196 + ... + 134352.

It is an arithmetic number, because the mean of its divisors is an integer number (796320).

Almost surely, 2^21081018 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21081018, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25482240).

21081018 is an abundant number, since it is smaller than the sum of its proper divisors (29883462).

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

21081018 is a wasteful number, since it uses less digits than its factorization.

21081018 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331.

The product of its (nonzero) digits is 128, while the sum is 21.

The square root of 21081018 is about 4591.4069739024. The cubic root of 21081018 is about 276.2467599928.

The spelling of 21081018 in words is "twenty-one million, eighty-one thousand, eighteen".