21689840 has 40 divisors (see below), whose sum is σ = 50822640. Its totient is φ = 8608256.

The previous prime is 21689827. The next prime is 21689867. The reversal of 21689840 is 4898612.

It is a tau number, because it is divible by the number of its divisors (40).

It is a junction number, because it is equal to n+sod(n) for n = 21689794 and 21689803.

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, 9971 + ... + 11949.

It is an arithmetic number, because the mean of its divisors is an integer number (1270566).

Almost surely, 2^21689840 is an apocalyptic number.

21689840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21689840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25411320).

21689840 is an abundant number, since it is smaller than the sum of its proper divisors (29132800).

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

21689840 is a wasteful number, since it uses less digits than its factorization.

21689840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2129 (or 2123 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 38.

The square root of 21689840 is about 4657.2352313363. The cubic root of 21689840 is about 278.8809073645.

The spelling of 21689840 in words is "twenty-one million, six hundred eighty-nine thousand, eight hundred forty".