21978147 has 8 divisors (see below), whose sum is σ = 29369344. Its totient is φ = 14619528.

The previous prime is 21978139. The next prime is 21978167. The reversal of 21978147 is 74187912.

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

It is not a de Polignac number, because 21978147 - 2³ = 21978139 is a prime.

It is a Duffinian 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, 6523 + ... + 9300.

It is an arithmetic number, because the mean of its divisors is an integer number (3671168).

Almost surely, 2^21978147 is an apocalyptic number.

21978147 is a deficient number, since it is larger than the sum of its proper divisors (7391197).

21978147 is a wasteful number, since it uses less digits than its factorization.

21978147 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 16289.

The product of its digits is 28224, while the sum is 39.

The square root of 21978147 is about 4688.0856434157. The cubic root of 21978147 is about 280.1111251090. Note that the first 4 decimals are identical.

The spelling of 21978147 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred forty-seven".