21541840 has 40 divisors (see below), whose sum is σ = 50844960. Its totient is φ = 8486016.

The previous prime is 21541829. The next prime is 21541841. The reversal of 21541840 is 4814512.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21541841) 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 7 ways as a sum of consecutive naturals, for example, 3351 + ... + 7369.

It is an arithmetic number, because the mean of its divisors is an integer number (1271124).

Almost surely, 2^21541840 is an apocalyptic number.

21541840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21541840 is the 2680-th octagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21541840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25422480).

21541840 is an abundant number, since it is smaller than the sum of its proper divisors (29303120).

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

21541840 is a wasteful number, since it uses less digits than its factorization.

21541840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4099 (or 4093 counting only the distinct ones).

The product of its (nonzero) digits is 1280, while the sum is 25.

The square root of 21541840 is about 4641.3187781061. The cubic root of 21541840 is about 278.2451471812.

The spelling of 21541840 in words is "twenty-one million, five hundred forty-one thousand, eight hundred forty".