21636378 has 48 divisors (see below), whose sum is σ = 48976200. Its totient is φ = 6894720.

The previous prime is 21636371. The next prime is 21636389. The reversal of 21636378 is 87363612.

It is a happy number.

21636378 is a `hidden beast` number, since 2 + 16 + 3 + 637 + 8 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 17363889 + 4272489 = 4167^2 + 2067^2 .

It is not an unprimeable number, because it can be changed into a prime (21636371) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 94368 + ... + 94596.

Almost surely, 2^21636378 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21636378, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24488100).

21636378 is an abundant number, since it is smaller than the sum of its proper divisors (27339822).

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

21636378 is a wasteful number, since it uses less digits than its factorization.

21636378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 447 (or 444 counting only the distinct ones).

The product of its digits is 36288, while the sum is 36.

The square root of 21636378 is about 4651.4920186968. The cubic root of 21636378 is about 278.6515865128.

The spelling of 21636378 in words is "twenty-one million, six hundred thirty-six thousand, three hundred seventy-eight".