21078819 has 8 divisors (see below), whose sum is σ = 31227920. Its totient is φ = 14052528.

The previous prime is 21078781. The next prime is 21078829. The reversal of 21078819 is 91887012.

It is not a de Polignac number, because 21078819 - 2⁹ = 21078307 is a prime.

It is a super-2 number, since 2×21078819² = 888633220869522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21078829) 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, 390322 + ... + 390375.

It is an arithmetic number, because the mean of its divisors is an integer number (3903490).

Almost surely, 2^21078819 is an apocalyptic number.

21078819 is a deficient number, since it is larger than the sum of its proper divisors (10149101).

21078819 is an equidigital number, since it uses as much as digits as its factorization.

21078819 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 780706 (or 780700 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21078819 is about 4591.1674985781. The cubic root of 21078819 is about 276.2371543886.

The spelling of 21078819 in words is "twenty-one million, seventy-eight thousand, eight hundred nineteen".