21051840 has 56 divisors (see below), whose sum is σ = 66842640. Its totient is φ = 5613568.

The previous prime is 21051839. The next prime is 21051847. The reversal of 21051840 is 4815012.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21051847) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10005 + ... + 11924.

Almost surely, 2^21051840 is an apocalyptic number.

21051840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21051840 is an abundant number, since it is smaller than the sum of its proper divisors (45790800).

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

21051840 is a wasteful number, since it uses less digits than its factorization.

21051840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21949 (or 21939 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 21.

The square root of 21051840 is about 4588.2284162844. The cubic root of 21051840 is about 276.1192511353.

Adding to 21051840 its reverse (4815012), we get a palindrome (25866852).

The spelling of 21051840 in words is "twenty-one million, fifty-one thousand, eight hundred forty".