21640661 has 8 divisors (see below), whose sum is σ = 25335744. Its totient is φ = 18096480.

The previous prime is 21640651. The next prime is 21640667. The reversal of 21640661 is 16604612.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21640661 - 2²² = 17446357 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21640661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21640667) 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 7 ways as a sum of consecutive naturals, for example, 37415 + ... + 37988.

It is an arithmetic number, because the mean of its divisors is an integer number (3166968).

Almost surely, 2^21640661 is an apocalyptic number.

It is an amenable number.

21640661 is a deficient number, since it is larger than the sum of its proper divisors (3695083).

21640661 is an equidigital number, since it uses as much as digits as its factorization.

21640661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 75451.

The product of its (nonzero) digits is 1728, while the sum is 26.

The square root of 21640661 is about 4651.9523858268. The cubic root of 21640661 is about 278.6699719992.

The spelling of 21640661 in words is "twenty-one million, six hundred forty thousand, six hundred sixty-one".