21140640 has 144 divisors (see below), whose sum is σ = 73768968. Its totient is φ = 5511168.

The previous prime is 21140633. The next prime is 21140663. The reversal of 21140640 is 4604112.

21140640 is a `hidden beast` number, since 21 + 1 + 4 + 0 + 640 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 15776784 + 5363856 = 3972^2 + 2316^2 .

It is a tau number, because it is divible by the number of its divisors (144).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 76182 + ... + 76458.

Almost surely, 2^21140640 is an apocalyptic number.

21140640 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 21140640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (36884484).

21140640 is an abundant number, since it is smaller than the sum of its proper divisors (52628328).

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

21140640 is a wasteful number, since it uses less digits than its factorization.

21140640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 351 (or 340 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21140640 is about 4597.8951706188. The cubic root of 21140640 is about 276.5069447923.

Adding to 21140640 its reverse (4604112), we get a palindrome (25744752).

The spelling of 21140640 in words is "twenty-one million, one hundred forty thousand, six hundred forty".