21078993 has 16 divisors (see below), whose sum is σ = 30413376. Its totient is φ = 12909120.

The previous prime is 21078991. The next prime is 21079007. The reversal of 21078993 is 39987012.

It is not a de Polignac number, because 21078993 - 2¹ = 21078991 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21078991) 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 15 ways as a sum of consecutive naturals, for example, 7663 + ... + 10043.

It is an arithmetic number, because the mean of its divisors is an integer number (1900836).

Almost surely, 2^21078993 is an apocalyptic number.

It is an amenable number.

21078993 is a deficient number, since it is larger than the sum of its proper divisors (9334383).

21078993 is a wasteful number, since it uses less digits than its factorization.

21078993 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2624.

The product of its (nonzero) digits is 27216, while the sum is 39.

The square root of 21078993 is about 4591.1864479675. The cubic root of 21078993 is about 276.2379144744.

The spelling of 21078993 in words is "twenty-one million, seventy-eight thousand, nine hundred ninety-three".