21237840 has 120 divisors (see below), whose sum is σ = 76844040. Its totient is φ = 5225472.

The previous prime is 21237793. The next prime is 21237841. The reversal of 21237840 is 4873212.

It can be written as a sum of positive squares in 4 ways, for example, as 553536 + 20684304 = 744^2 + 4548^2 .

It is a tau number, because it is divible by the number of its divisors (120).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21237841) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 8226 + ... + 10494.

It is an arithmetic number, because the mean of its divisors is an integer number (640367).

Almost surely, 2^21237840 is an apocalyptic number.

21237840 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 21237840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38422020).

21237840 is an abundant number, since it is smaller than the sum of its proper divisors (55606200).

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

21237840 is a wasteful number, since it uses less digits than its factorization.

21237840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2301 (or 2292 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21237840 is about 4608.4531027233. The cubic root of 21237840 is about 276.9300696240.

The spelling of 21237840 in words is "twenty-one million, two hundred thirty-seven thousand, eight hundred forty".