21645378 has 24 divisors (see below), whose sum is σ = 48412416. Its totient is φ = 6982200.

The previous prime is 21645373. The next prime is 21645413. The reversal of 21645378 is 87354612.

21645378 is a `hidden beast` number, since 2 + 1 + 645 + 3 + 7 + 8 = 666.

It is not an unprimeable number, because it can be changed into a prime (21645373) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18838 + ... + 19953.

It is an arithmetic number, because the mean of its divisors is an integer number (2017184).

Almost surely, 2^21645378 is an apocalyptic number.

21645378 is an abundant number, since it is smaller than the sum of its proper divisors (26767038).

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

21645378 is a wasteful number, since it uses less digits than its factorization.

21645378 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38830 (or 38827 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21645378 is about 4652.4593496343. The cubic root of 21645378 is about 278.6902176957.

The spelling of 21645378 in words is "twenty-one million, six hundred forty-five thousand, three hundred seventy-eight".