21640040 has 16 divisors (see below), whose sum is σ = 48690180. Its totient is φ = 8656000.

The previous prime is 21640039. The next prime is 21640049. The reversal of 21640040 is 4004612.

It can be written as a sum of positive squares in 2 ways, for example, as 21141604 + 498436 = 4598^2 + 706^2 .

It is not an unprimeable number, because it can be changed into a prime (21640049) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 270461 + ... + 270540.

Almost surely, 2^21640040 is an apocalyptic number.

21640040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21640040 is an abundant number, since it is smaller than the sum of its proper divisors (27050140).

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

21640040 is a wasteful number, since it uses less digits than its factorization.

21640040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 541012 (or 541008 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 17.

The square root of 21640040 is about 4651.8856391790. The cubic root of 21640040 is about 278.6673064043.

Adding to 21640040 its reverse (4004612), we get a palindrome (25644652).

The spelling of 21640040 in words is "twenty-one million, six hundred forty thousand, forty".