21681678 has 16 divisors (see below), whose sum is σ = 43557120. Its totient is φ = 7194936.

The previous prime is 21681659. The next prime is 21681683. The reversal of 21681678 is 87618612.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 6598 + ... + 9321.

It is an arithmetic number, because the mean of its divisors is an integer number (2722320).

Almost surely, 2^21681678 is an apocalyptic number.

21681678 is an abundant number, since it is smaller than the sum of its proper divisors (21875442).

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

21681678 is a wasteful number, since it uses less digits than its factorization.

21681678 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16151.

The product of its digits is 32256, while the sum is 39.

The square root of 21681678 is about 4656.3588779217. The cubic root of 21681678 is about 278.8459215286.

The spelling of 21681678 in words is "twenty-one million, six hundred eighty-one thousand, six hundred seventy-eight".