16221408711561 has 15 divisors (see below), whose sum is σ = 24232035063511. Its totient is φ = 10814248308888.

The previous prime is 16221408711551. The next prime is 16221408711659. The reversal of 16221408711561 is 16511780412261.

It is a happy number.

The square root of 16221408711561 is 4027581.

It is a perfect power (a square), and thus also a powerful number.

16221408711561 is a `hidden beast` number, since 1 + 6 + 2 + 2 + 1 + 4 + 0 + 87 + 1 + 1 + 561 = 666.

It can be written as a sum of positive squares in only one way, i.e., 12301721479161 + 3919687232400 = 3507381^2 + 1979820^2 .

It is a de Polignac number, because none of the positive numbers 2^k-16221408711561 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (16221408711551) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 36024475 + ... + 36471983.

Almost surely, 2^{16221408711561} is an apocalyptic number.

16221408711561 is the 4027581-st square number.

16221408711561 is the 2013791-st centered octagonal number.

It is an amenable number.

16221408711561 is a deficient number, since it is larger than the sum of its proper divisors (8010626351950).

16221408711561 is an frugal number, since it uses more digits than its factorization.

16221408711561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 895030 (or 447512 counting only the distinct ones).

The product of its (nonzero) digits is 161280, while the sum is 45.

The spelling of 16221408711561 in words is "sixteen trillion, two hundred twenty-one billion, four hundred eight million, seven hundred eleven thousand, five hundred sixty-one".