21684340 has 12 divisors (see below), whose sum is σ = 45537156. Its totient is φ = 8673728.

The previous prime is 21684319. The next prime is 21684347. The reversal of 21684340 is 4348612.

It can be written as a sum of positive squares in 2 ways, for example, as 9809424 + 11874916 = 3132^2 + 3446^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21684299 and 21684308.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21684347) 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 3 ways as a sum of consecutive naturals, for example, 542089 + ... + 542128.

It is an arithmetic number, because the mean of its divisors is an integer number (3794763).

Almost surely, 2^21684340 is an apocalyptic number.

21684340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21684340 is an abundant number, since it is smaller than the sum of its proper divisors (23852816).

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

21684340 is a wasteful number, since it uses less digits than its factorization.

21684340 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1084226 (or 1084224 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 28.

The square root of 21684340 is about 4656.6447148134. The cubic root of 21684340 is about 278.8573329681.

The spelling of 21684340 in words is "twenty-one million, six hundred eighty-four thousand, three hundred forty".