21173840 has 40 divisors (see below), whose sum is σ = 52128360. Its totient is φ = 7970816.

The previous prime is 21173807. The next prime is 21173849. The reversal of 21173840 is 4837112.

21173840 is nontrivially palindromic in base 14.

It can be written as a sum of positive squares in 4 ways, for example, as 3297856 + 17875984 = 1816^2 + 4228^2 .

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 (21173849) 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, 6425 + ... + 9144.

It is an arithmetic number, because the mean of its divisors is an integer number (1303209).

Almost surely, 2^21173840 is an apocalyptic number.

21173840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21173840 is an abundant number, since it is smaller than the sum of its proper divisors (30954520).

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

21173840 is a wasteful number, since it uses less digits than its factorization.

21173840 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15599 (or 15593 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 21173840 is about 4601.5041019215. The cubic root of 21173840 is about 276.6516144776.

The spelling of 21173840 in words is "twenty-one million, one hundred seventy-three thousand, eight hundred forty".