21688542 has 24 divisors (see below), whose sum is σ = 47412144. Its totient is φ = 7164864.

The previous prime is 21688531. The next prime is 21688543. The reversal of 21688542 is 24588612.

It is a junction number, because it is equal to n+sod(n) for n = 21688497 and 21688506.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21688543) 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, 3298 + ... + 7365.

It is an arithmetic number, because the mean of its divisors is an integer number (1975506).

Almost surely, 2^21688542 is an apocalyptic number.

21688542 is an abundant number, since it is smaller than the sum of its proper divisors (25723602).

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

21688542 is a wasteful number, since it uses less digits than its factorization.

21688542 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10784 (or 10781 counting only the distinct ones).

The product of its digits is 30720, while the sum is 36.

The square root of 21688542 is about 4657.0958761872. The cubic root of 21688542 is about 278.8753441662.

The spelling of 21688542 in words is "twenty-one million, six hundred eighty-eight thousand, five hundred forty-two".