21978861 has 8 divisors (see below), whose sum is σ = 29590080. Its totient is φ = 14510112.

The previous prime is 21978799. The next prime is 21978871. The reversal of 21978861 is 16887912.

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

It is not a de Polignac number, because 21978861 - 2¹¹ = 21976813 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978871) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 35256 + ... + 35873.

It is an arithmetic number, because the mean of its divisors is an integer number (3698760).

Almost surely, 2^21978861 is an apocalyptic number.

It is an amenable number.

21978861 is a deficient number, since it is larger than the sum of its proper divisors (7611219).

21978861 is a wasteful number, since it uses less digits than its factorization.

21978861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 71235.

The product of its digits is 48384, while the sum is 42.

The square root of 21978861 is about 4688.1617932832. The cubic root of 21978861 is about 280.1141583823.

The spelling of 21978861 in words is "twenty-one million, nine hundred seventy-eight thousand, eight hundred sixty-one".