21604153561 has 4 divisors (see below), whose sum is σ = 21614866612. Its totient is φ = 21593440512.

The previous prime is 21604153481. The next prime is 21604153573. The reversal of 21604153561 is 16535140612.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 10295957961 + 11308195600 = 101469^2 + 106340^2 .

It is a cyclic number.

It is not a de Polignac number, because 21604153561 - 2⁹ = 21604153049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21604153861) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5353500 + ... + 5357533.

It is an arithmetic number, because the mean of its divisors is an integer number (5403716653).

Almost surely, 2^21604153561 is an apocalyptic number.

It is an amenable number.

21604153561 is a deficient number, since it is larger than the sum of its proper divisors (10713051).

21604153561 is a wasteful number, since it uses less digits than its factorization.

21604153561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10713050.

The product of its (nonzero) digits is 21600, while the sum is 34.

The spelling of 21604153561 in words is "twenty-one billion, six hundred four million, one hundred fifty-three thousand, five hundred sixty-one".