16561634421 has 8 divisors (see below), whose sum is σ = 22082780704. Its totient is φ = 11040788880.

The previous prime is 16561634407. The next prime is 16561634429. The reversal of 16561634421 is 12443616561.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 16561634421 - 2¹⁸ = 16561372277 is a prime.

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 16561634421.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16561634429) 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, 147735 + ... + 234411.

It is an arithmetic number, because the mean of its divisors is an integer number (2760347588).

Almost surely, 2^16561634421 is an apocalyptic number.

It is an amenable number.

16561634421 is a deficient number, since it is larger than the sum of its proper divisors (5521146283).

16561634421 is an equidigital number, since it uses as much as digits as its factorization.

16561634421 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 150371.

The product of its digits is 103680, while the sum is 39.

The spelling of 16561634421 in words is "sixteen billion, five hundred sixty-one million, six hundred thirty-four thousand, four hundred twenty-one".