21605461221 has 4 divisors (see below), whose sum is σ = 28807281632. Its totient is φ = 14403640812.

The previous prime is 21605461153. The next prime is 21605461231. The reversal of 21605461221 is 12216450612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 21605461221 - 2¹⁰ = 21605460197 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 (21605461231) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3600910201 + ... + 3600910206.

It is an arithmetic number, because the mean of its divisors is an integer number (7201820408).

Almost surely, 2^21605461221 is an apocalyptic number.

It is an amenable number.

21605461221 is a deficient number, since it is larger than the sum of its proper divisors (7201820411).

21605461221 is an equidigital number, since it uses as much as digits as its factorization.

21605461221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7201820410.

The product of its (nonzero) digits is 5760, while the sum is 30.

The spelling of 21605461221 in words is "twenty-one billion, six hundred five million, four hundred sixty-one thousand, two hundred twenty-one".