21175840 has 144 divisors (see below), whose sum is σ = 60587352. Its totient is φ = 6967296.

The previous prime is 21175837. The next prime is 21175849. The reversal of 21175840 is 4857112.

It can be written as a sum of positive squares in 4 ways, for example, as 20322064 + 853776 = 4508^2 + 924^2 .

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 = 21175799 and 21175808.

It is not an unprimeable number, because it can be changed into a prime (21175849) 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, 290044 + ... + 290116.

Almost surely, 2^21175840 is an apocalyptic number.

21175840 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 21175840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30293676).

21175840 is an abundant number, since it is smaller than the sum of its proper divisors (39411512).

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

21175840 is a wasteful number, since it uses less digits than its factorization.

21175840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 139 (or 124 counting only the distinct ones).

The product of its (nonzero) digits is 2240, while the sum is 28.

The square root of 21175840 is about 4601.7214170352. The cubic root of 21175840 is about 276.6603246881.

The spelling of 21175840 in words is "twenty-one million, one hundred seventy-five thousand, eight hundred forty".