21397878 has 32 divisors (see below), whose sum is σ = 48568320. Its totient is φ = 6980040.

The previous prime is 21397867. The next prime is 21397879. The reversal of 21397878 is 87879312.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21397879) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1678 + ... + 6753.

It is an arithmetic number, because the mean of its divisors is an integer number (1517760).

Almost surely, 2^21397878 is an apocalyptic number.

21397878 is an abundant number, since it is smaller than the sum of its proper divisors (27170442).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21397878 is a wasteful number, since it uses less digits than its factorization.

21397878 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8489 (or 8483 counting only the distinct ones).

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

The square root of 21397878 is about 4625.7840416518. The cubic root of 21397878 is about 277.6239329553.

The spelling of 21397878 in words is "twenty-one million, three hundred ninety-seven thousand, eight hundred seventy-eight".