15565551665561 has 4 divisors (see below), whose sum is σ = 15566267772852. Its totient is φ = 15564835558272.

The previous prime is 15565551665527. The next prime is 15565551665579. The reversal of 15565551665561 is 16556615556551.

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 650855243536 + 14914696422025 = 806756^2 + 3861955^2 .

It is a cyclic number.

It is not a de Polignac number, because 15565551665561 - 2¹⁸ = 15565551403417 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 15565551665494 and 15565551665503.

It is not an unprimeable number, because it can be changed into a prime (15565551665581) 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, 358021040 + ... + 358064513.

It is an arithmetic number, because the mean of its divisors is an integer number (3891566943213).

Almost surely, 2^{15565551665561} is an apocalyptic number.

It is an amenable number.

15565551665561 is a deficient number, since it is larger than the sum of its proper divisors (716107291).

15565551665561 is an equidigital number, since it uses as much as digits as its factorization.

15565551665561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 716107290.

The product of its digits is 101250000, while the sum is 62.

The spelling of 15565551665561 in words is "fifteen trillion, five hundred sixty-five billion, five hundred fifty-one million, six hundred sixty-five thousand, five hundred sixty-one".