15663561 has 4 divisors (see below), whose sum is σ = 20884752. Its totient is φ = 10442372.

The previous prime is 15663553. The next prime is 15663563. The reversal of 15663561 is 16536651.

15663561 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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 15663561 - 2³ = 15663553 is a prime.

It is not an unprimeable number, because it can be changed into a prime (15663563) 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, 2610591 + ... + 2610596.

It is an arithmetic number, because the mean of its divisors is an integer number (5221188).

Almost surely, 2^15663561 is an apocalyptic number.

It is an amenable number.

15663561 is a deficient number, since it is larger than the sum of its proper divisors (5221191).

15663561 is an equidigital number, since it uses as much as digits as its factorization.

15663561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5221190.

The product of its digits is 16200, while the sum is 33.

The square root of 15663561 is about 3957.7216930957. The cubic root of 15663561 is about 250.2054897163.

The spelling of 15663561 in words is "fifteen million, six hundred sixty-three thousand, five hundred sixty-one".