21021565661 has 8 divisors (see below), whose sum is σ = 21054860064. Its totient is φ = 20988296560.

The previous prime is 21021565627. The next prime is 21021565673. The reversal of 21021565661 is 16656512012.

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 21021565661 - 2³⁰ = 19947823837 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 (21021565261) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2250146 + ... + 2259468.

It is an arithmetic number, because the mean of its divisors is an integer number (2631857508).

Almost surely, 2^21021565661 is an apocalyptic number.

It is an amenable number.

21021565661 is a deficient number, since it is larger than the sum of its proper divisors (33294403).

21021565661 is an equidigital number, since it uses as much as digits as its factorization.

21021565661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12651.

The product of its (nonzero) digits is 21600, while the sum is 35.

The spelling of 21021565661 in words is "twenty-one billion, twenty-one million, five hundred sixty-five thousand, six hundred sixty-one".