1561501555 has 4 divisors (see below), whose sum is σ = 1873801872. Its totient is φ = 1249201240.

The previous prime is 1561501541. The next prime is 1561501559. The reversal of 1561501555 is 5551051651.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 1561501555 - 2¹⁷ = 1561370483 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 1561501555.

It is not an unprimeable number, because it can be changed into a prime (1561501559) 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, 156150151 + ... + 156150160.

It is an arithmetic number, because the mean of its divisors is an integer number (468450468).

Almost surely, 2^1561501555 is an apocalyptic number.

1561501555 is a deficient number, since it is larger than the sum of its proper divisors (312300317).

1561501555 is an equidigital number, since it uses as much as digits as its factorization.

1561501555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 312300316.

The product of its (nonzero) digits is 18750, while the sum is 34.

The square root of 1561501555 is about 39515.8392926178. The cubic root of 1561501555 is about 1160.1499892756.

The spelling of 1561501555 in words is "one billion, five hundred sixty-one million, five hundred one thousand, five hundred fifty-five".