21640861 has 12 divisors (see below), whose sum is σ = 24685920. Its totient is φ = 18813080.

The previous prime is 21640849. The next prime is 21640877. The reversal of 21640861 is 16804612.

It is a de Polignac number, because none of the positive numbers 2^k-21640861 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640811) 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 11 ways as a sum of consecutive naturals, for example, 3960 + ... + 7678.

It is an arithmetic number, because the mean of its divisors is an integer number (2057160).

Almost surely, 2^21640861 is an apocalyptic number.

It is an amenable number.

21640861 is a deficient number, since it is larger than the sum of its proper divisors (3045059).

21640861 is a wasteful number, since it uses less digits than its factorization.

21640861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3776 (or 3753 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 28.

The square root of 21640861 is about 4651.9738821279. The cubic root of 21640861 is about 278.6708304731.

The spelling of 21640861 in words is "twenty-one million, six hundred forty thousand, eight hundred sixty-one".