21978667 has 4 divisors (see below), whose sum is σ = 21988120. Its totient is φ = 21969216.

The previous prime is 21978661. The next prime is 21978673. The reversal of 21978667 is 76687912.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is an interprime number because it is at equal distance from previous prime (21978661) and next prime (21978673).

It is a cyclic number.

It is not a de Polignac number, because 21978667 - 2¹⁹ = 21454379 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21978661) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1468 + ... + 6790.

It is an arithmetic number, because the mean of its divisors is an integer number (5497030).

Almost surely, 2^21978667 is an apocalyptic number.

21978667 is a deficient number, since it is larger than the sum of its proper divisors (9453).

21978667 is an equidigital number, since it uses as much as digits as its factorization.

21978667 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9452.

The product of its digits is 254016, while the sum is 46.

The square root of 21978667 is about 4688.1411028253. The cubic root of 21978667 is about 280.1133342221.

The spelling of 21978667 in words is "twenty-one million, nine hundred seventy-eight thousand, six hundred sixty-seven".