5661606721 has 4 divisors (see below), whose sum is σ = 5662567872. Its totient is φ = 5660645572.

The previous prime is 5661606593. The next prime is 5661606749. The reversal of 5661606721 is 1276061665.

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, and also an emirpimes, since its reverse is a distinct semiprime: 1276061665 = 5 ⋅255212333.

It is a cyclic number.

It is not a de Polignac number, because 5661606721 - 2⁷ = 5661606593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (5661606521) 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, 471685 + ... + 483538.

It is an arithmetic number, because the mean of its divisors is an integer number (1415641968).

Almost surely, 2^5661606721 is an apocalyptic number.

It is an amenable number.

5661606721 is a deficient number, since it is larger than the sum of its proper divisors (961151).

5661606721 is an equidigital number, since it uses as much as digits as its factorization.

5661606721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 961150.

The product of its (nonzero) digits is 90720, while the sum is 40.

The square root of 5661606721 is about 75243.6490409656. The cubic root of 5661606721 is about 1782.2962748519.

The spelling of 5661606721 in words is "five billion, six hundred sixty-one million, six hundred six thousand, seven hundred twenty-one".