15987561 has 4 divisors (see below), whose sum is σ = 21316752. Its totient is φ = 10658372.

The previous prime is 15987533. The next prime is 15987563. The reversal of 15987561 is 16578951.

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 15987561 - 2¹⁵ = 15954793 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (15987563) 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, 2664591 + ... + 2664596.

It is an arithmetic number, because the mean of its divisors is an integer number (5329188).

Almost surely, 2^15987561 is an apocalyptic number.

It is an amenable number.

15987561 is a deficient number, since it is larger than the sum of its proper divisors (5329191).

15987561 is an equidigital number, since it uses as much as digits as its factorization.

15987561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5329190.

The product of its digits is 75600, while the sum is 42.

The square root of 15987561 is about 3998.4448226779. Note that the first 3 decimals coincide. The cubic root of 15987561 is about 251.9188923912.

The spelling of 15987561 in words is "fifteen million, nine hundred eighty-seven thousand, five hundred sixty-one".