21978133 has 8 divisors (see below), whose sum is σ = 23007168. Its totient is φ = 20955264.

The previous prime is 21978109. The next prime is 21978137. The reversal of 21978133 is 33187912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a 4-Lehmer number, since φ(21978133) divides (21978133-1)⁴.

It is a cyclic number.

It is not a de Polignac number, because 21978133 - 2¹⁷ = 21847061 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978137) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6766 + ... + 9472.

It is an arithmetic number, because the mean of its divisors is an integer number (2875896).

Almost surely, 2^21978133 is an apocalyptic number.

21978133 is a gapful number since it is divisible by the number (23) formed by its first and last digit.

21978133 is the 2707-th octagonal number.

It is an amenable number.

21978133 is a deficient number, since it is larger than the sum of its proper divisors (1029035).

21978133 is a wasteful number, since it uses less digits than its factorization.

21978133 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3083.

The product of its digits is 9072, while the sum is 34.

The square root of 21978133 is about 4688.0841502686. The cubic root of 21978133 is about 280.1110656324. Note that the first 3 decimals are identical.

The spelling of 21978133 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred thirty-three".