21978253 has 4 divisors (see below), whose sum is σ = 23976288. Its totient is φ = 19980220.

The previous prime is 21978251. The next prime is 21978293. The reversal of 21978253 is 35287912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21978253 - 2¹ = 21978251 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 (21978251) 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, 999001 + ... + 999022.

It is an arithmetic number, because the mean of its divisors is an integer number (5994072).

Almost surely, 2^21978253 is an apocalyptic number.

It is an amenable number.

21978253 is a deficient number, since it is larger than the sum of its proper divisors (1998035).

21978253 is a wasteful number, since it uses less digits than its factorization.

21978253 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1998034.

The product of its digits is 30240, while the sum is 37.

The square root of 21978253 is about 4688.0969486562. The cubic root of 21978253 is about 280.1115754311. Note that the first 3 decimals are identical.

The spelling of 21978253 in words is "twenty-one million, nine hundred seventy-eight thousand, two hundred fifty-three".