21078 has 12 divisors (see below), whose sum is σ = 45708. Its totient is φ = 7020.

The previous prime is 21067. The next prime is 21089. The reversal of 21078 is 87012.

It is an interprime number because it is at equal distance from previous prime (21067) and next prime (21089).

It is a Smith number, since the sum of its digits (18) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (18), and also a Moran number because the ratio is a prime number: 1171 = 21078 / (2 + 1 + 0 + 7 + 8).

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

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21078.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 568 + ... + 603.

It is an arithmetic number, because the mean of its divisors is an integer number (3809).

2²¹⁰⁷⁸ is an apocalyptic number.

21078 is an abundant number, since it is smaller than the sum of its proper divisors (24630).

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

21078 is a wasteful number, since it uses less digits than its factorization.

21078 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1179 (or 1176 counting only the distinct ones).

The product of its (nonzero) digits is 112, while the sum is 18.

The square root of 21078 is about 145.1826435908. The cubic root of 21078 is about 27.6233576687.

The spelling of 21078 in words is "twenty-one thousand, seventy-eight".