21185640 has 144 divisors (see below), whose sum is σ = 80161380. Its totient is φ = 4838400.

The previous prime is 21185639. The next prime is 21185641. The reversal of 21185640 is 4658112.

21185640 is a `hidden beast` number, since 2 + 1 + 18 + 5 + 640 = 666.

It is an interprime number because it is at equal distance from previous prime (21185639) and next prime (21185641).

It can be written as a sum of positive squares in 2 ways, for example, as 17288964 + 3896676 = 4158^2 + 1974^2 .

It is not an unprimeable number, because it can be changed into a prime (21185641) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 17040 + ... + 18240.

Almost surely, 2^21185640 is an apocalyptic number.

21185640 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 21185640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (40080690).

21185640 is an abundant number, since it is smaller than the sum of its proper divisors (58975740).

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

21185640 is a wasteful number, since it uses less digits than its factorization.

21185640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1232 (or 1218 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21185640 is about 4602.7861127800. The cubic root of 21185640 is about 276.7029967936.

The spelling of 21185640 in words is "twenty-one million, one hundred eighty-five thousand, six hundred forty".