21100004561 has 4 divisors (see below), whose sum is σ = 21103752000. Its totient is φ = 21096257124.

The previous prime is 21100004557. The next prime is 21100004587. The reversal of 21100004561 is 16540000112.

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 21100004561 - 2² = 21100004557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21100004161) 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, 1865261 + ... + 1876538.

It is an arithmetic number, because the mean of its divisors is an integer number (5275938000).

Almost surely, 2^21100004561 is an apocalyptic number.

It is an amenable number.

21100004561 is a deficient number, since it is larger than the sum of its proper divisors (3747439).

21100004561 is an equidigital number, since it uses as much as digits as its factorization.

21100004561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3747438.

The product of its (nonzero) digits is 240, while the sum is 20.

Adding to 21100004561 its reverse (16540000112), we get a palindrome (37640004673).

The spelling of 21100004561 in words is "twenty-one billion, one hundred million, four thousand, five hundred sixty-one".