21073831561 has 4 divisors (see below), whose sum is σ = 21225442000. Its totient is φ = 20922221124.

The previous prime is 21073831529. The next prime is 21073831609. The reversal of 21073831561 is 16513837012.

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 a cyclic number.

It is not a de Polignac number, because 21073831561 - 2⁵ = 21073831529 is a prime.

It is a super-2 number, since 2×21073831561² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21073831561.

It is not an unprimeable number, because it can be changed into a prime (21073831511) 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, 75805011 + ... + 75805288.

It is an arithmetic number, because the mean of its divisors is an integer number (5306360500).

Almost surely, 2^21073831561 is an apocalyptic number.

It is an amenable number.

21073831561 is a deficient number, since it is larger than the sum of its proper divisors (151610439).

21073831561 is a wasteful number, since it uses less digits than its factorization.

21073831561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 151610438.

The product of its (nonzero) digits is 30240, while the sum is 37.

The spelling of 21073831561 in words is "twenty-one billion, seventy-three million, eight hundred thirty-one thousand, five hundred sixty-one".