21878397 has 16 divisors (see below), whose sum is σ = 32719680. Its totient is φ = 14447376.

The previous prime is 21878369. The next prime is 21878401. The reversal of 21878397 is 79387812.

It is not a de Polignac number, because 21878397 - 2²⁰ = 20829821 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21878327) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 898 + ... + 6675.

It is an arithmetic number, because the mean of its divisors is an integer number (2044980).

Almost surely, 2^21878397 is an apocalyptic number.

21878397 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21878397 is a deficient number, since it is larger than the sum of its proper divisors (10841283).

21878397 is a wasteful number, since it uses less digits than its factorization.

21878397 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7689 (or 7683 counting only the distinct ones).

The product of its digits is 169344, while the sum is 45.

The square root of 21878397 is about 4677.4348739453. The cubic root of 21878397 is about 279.6867116714.

The spelling of 21878397 in words is "twenty-one million, eight hundred seventy-eight thousand, three hundred ninety-seven".