21978019 has 6 divisors (see below), whose sum is σ = 25566324. Its totient is φ = 18838260.

The previous prime is 21978017. The next prime is 21978023. The reversal of 21978019 is 91087912.

It is not a de Polignac number, because 21978019 - 2¹ = 21978017 is a prime.

It is a super-2 number, since 2×21978019² = 966066638328722, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21978017) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 224217 + ... + 224314.

It is an arithmetic number, because the mean of its divisors is an integer number (4261054).

Almost surely, 2^21978019 is an apocalyptic number.

21978019 is a deficient number, since it is larger than the sum of its proper divisors (3588305).

21978019 is an equidigital number, since it uses as much as digits as its factorization.

21978019 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 448545 (or 448538 counting only the distinct ones).

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21978019 is about 4688.0719917680. The cubic root of 21978019 is about 280.1105813220.

The spelling of 21978019 in words is "twenty-one million, nine hundred seventy-eight thousand, nineteen".