21878424 has 80 divisors (see below), whose sum is σ = 64541400. Its totient is φ = 6905088.

The previous prime is 21878419. The next prime is 21878429. The reversal of 21878424 is 42487812.

It is an interprime number because it is at equal distance from previous prime (21878419) and next prime (21878429).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21878429) 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 19 ways as a sum of consecutive naturals, for example, 11424 + ... + 13200.

Almost surely, 2^21878424 is an apocalyptic number.

21878424 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21878424, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32270700).

21878424 is an abundant number, since it is smaller than the sum of its proper divisors (42662976).

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

21878424 is a wasteful number, since it uses less digits than its factorization.

21878424 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1814 (or 1801 counting only the distinct ones).

The product of its digits is 28672, while the sum is 36.

The square root of 21878424 is about 4677.4377601418. The cubic root of 21878424 is about 279.6868267246.

The spelling of 21878424 in words is "twenty-one million, eight hundred seventy-eight thousand, four hundred twenty-four".