21678228 has 72 divisors (see below), whose sum is σ = 64393056. Its totient is φ = 6062400.

The previous prime is 21678211. The next prime is 21678253. The reversal of 21678228 is 82287612.

It is a happy number.

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

It is a junction number, because it is equal to n+sod(n) for n = 21678192 and 21678201.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 3043 + ... + 7253.

It is an arithmetic number, because the mean of its divisors is an integer number (894348).

Almost surely, 2^21678228 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21678228, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32196528).

21678228 is an abundant number, since it is smaller than the sum of its proper divisors (42714828).

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

21678228 is a wasteful number, since it uses less digits than its factorization.

21678228 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4245 (or 4240 counting only the distinct ones).

The product of its digits is 21504, while the sum is 36.

The square root of 21678228 is about 4655.9884020474. The cubic root of 21678228 is about 278.8311307076.

The spelling of 21678228 in words is "twenty-one million, six hundred seventy-eight thousand, two hundred twenty-eight".