21978171 has 6 divisors (see below), whose sum is σ = 31746260. Its totient is φ = 14652108.

The previous prime is 21978169. The next prime is 21978181. The reversal of 21978171 is 17187912.

It is not a de Polignac number, because 21978171 - 2¹ = 21978169 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21978181) 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, 1221001 + ... + 1221018.

Almost surely, 2^21978171 is an apocalyptic number.

21978171 is a deficient number, since it is larger than the sum of its proper divisors (9768089).

21978171 is a wasteful number, since it uses less digits than its factorization.

21978171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2442025 (or 2442022 counting only the distinct ones).

The product of its digits is 7056, while the sum is 36.

The square root of 21978171 is about 4688.0882030952. The cubic root of 21978171 is about 280.1112270689. Note that the first 3 decimals are identical.

The spelling of 21978171 in words is "twenty-one million, nine hundred seventy-eight thousand, one hundred seventy-one".