2100506561 has 4 divisors (see below), whose sum is σ = 2100652500. Its totient is φ = 2100360624.

The previous prime is 2100506557. The next prime is 2100506581. The reversal of 2100506561 is 1656050012.

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 1199306161 + 901200400 = 34631^2 + 30020^2 .

It is a cyclic number.

It is not a de Polignac number, because 2100506561 - 2² = 2100506557 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 2100506561.

It is not an unprimeable number, because it can be changed into a prime (2100506581) 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, 48686 + ... + 81063.

It is an arithmetic number, because the mean of its divisors is an integer number (525163125).

Almost surely, 2^2100506561 is an apocalyptic number.

It is an amenable number.

2100506561 is a deficient number, since it is larger than the sum of its proper divisors (145939).

2100506561 is a wasteful number, since it uses less digits than its factorization.

2100506561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 145938.

The product of its (nonzero) digits is 1800, while the sum is 26.

The square root of 2100506561 is about 45831.2836499263. The cubic root of 2100506561 is about 1280.6821236082.

Adding to 2100506561 its reverse (1656050012), we get a palindrome (3756556573).

The spelling of 2100506561 in words is "two billion, one hundred million, five hundred six thousand, five hundred sixty-one".