21891040 has 72 divisors (see below), whose sum is σ = 54726840. Its totient is φ = 8273664.

The previous prime is 21891031. The next prime is 21891041. The reversal of 21891040 is 4019812.

It is a happy number.

It is a junction number, because it is equal to n+sod(n) for n = 21890996 and 21891014.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21891041) 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 11 ways as a sum of consecutive naturals, for example, 57571 + ... + 57949.

It is an arithmetic number, because the mean of its divisors is an integer number (760095).

Almost surely, 2^21891040 is an apocalyptic number.

21891040 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 21891040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27363420).

21891040 is an abundant number, since it is smaller than the sum of its proper divisors (32835800).

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

21891040 is a wasteful number, since it uses less digits than its factorization.

21891040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 432 (or 405 counting only the distinct ones).

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 21891040 is about 4678.7861673729. The cubic root of 21891040 is about 279.7405760408.

The spelling of 21891040 in words is "twenty-one million, eight hundred ninety-one thousand, forty".