21742840 has 128 divisors (see below), whose sum is σ = 60710400. Its totient is φ = 6842880.

The previous prime is 21742829. The next prime is 21742913. The reversal of 21742840 is 4824712.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a junction number, because it is equal to n+sod(n) for n = 21742799 and 21742808.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 324487 + ... + 324553.

It is an arithmetic number, because the mean of its divisors is an integer number (474300).

Almost surely, 2^21742840 is an apocalyptic number.

21742840 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 21742840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30355200).

21742840 is an abundant number, since it is smaller than the sum of its proper divisors (38967560).

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

21742840 is a wasteful number, since it uses less digits than its factorization.

21742840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 165 (or 161 counting only the distinct ones).

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21742840 is about 4662.9218307838. The cubic root of 21742840 is about 279.1078748500.

The spelling of 21742840 in words is "twenty-one million, seven hundred forty-two thousand, eight hundred forty".