21018 has 16 divisors (see below), whose sum is σ = 43776. Its totient is φ = 6720.

The previous prime is 21017. The next prime is 21019. The reversal of 21018 is 81012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21017) and next prime (21019).

It is an alternating number because its digits alternate between even and odd.

21018 is an undulating number in base 15.

It is a junction number, because it is equal to n+sod(n) for n = 20994 and 21012.

It is not an unprimeable number, because it can be changed into a prime (21011) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 130 + ... + 242.

It is an arithmetic number, because the mean of its divisors is an integer number (2736).

2²¹⁰¹⁸ is an apocalyptic number.

21018 is an abundant number, since it is smaller than the sum of its proper divisors (22758).

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

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (21888).

21018 is a wasteful number, since it uses less digits than its factorization.

21018 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 149.

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 21018 is about 144.9758600595. The cubic root of 21018 is about 27.5971221532.

The spelling of 21018 in words is "twenty-one thousand, eighteen".