21640064 has 16 divisors (see below), whose sum is σ = 43111320. Its totient is φ = 10819968.

The previous prime is 21640063. The next prime is 21640067. The reversal of 21640064 is 46004612.

It is a happy number.

It is a tau number, because it is divible by the number of its divisors (16).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640063) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 84404 + ... + 84659.

Almost surely, 2^21640064 is an apocalyptic number.

It is an amenable number.

21640064 is a deficient number, since it is larger than the sum of its proper divisors (21471256).

21640064 is an equidigital number, since it uses as much as digits as its factorization.

21640064 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 169077 (or 169065 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 23.

The square root of 21640064 is about 4651.8882187774. Note that the first 3 decimals coincide. The cubic root of 21640064 is about 278.6674094234.

Adding to 21640064 its reverse (46004612), we get a palindrome (67644676).

The spelling of 21640064 in words is "twenty-one million, six hundred forty thousand, sixty-four".