21640915 has 16 divisors (see below), whose sum is σ = 28086912. Its totient is φ = 15944704.

The previous prime is 21640891. The next prime is 21640919. The reversal of 21640915 is 51904612.

It is a cyclic number.

It is not a de Polignac number, because 21640915 - 2¹¹ = 21638867 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21640919) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1287 + ... + 6703.

It is an arithmetic number, because the mean of its divisors is an integer number (1755432).

Almost surely, 2^21640915 is an apocalyptic number.

21640915 is a deficient number, since it is larger than the sum of its proper divisors (6445997).

21640915 is a wasteful number, since it uses less digits than its factorization.

21640915 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5486.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21640915 is about 4651.9796861121. The cubic root of 21640915 is about 278.6710622601.

The spelling of 21640915 in words is "twenty-one million, six hundred forty thousand, nine hundred fifteen".