1661607553 has 4 divisors (see below), whose sum is σ = 1682640640. Its totient is φ = 1640574468.

The previous prime is 1661607511. The next prime is 1661607559. The reversal of 1661607553 is 3557061661.

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: 3557061661 = 47 ⋅75682163.

It is a cyclic number.

It is not a de Polignac number, because 1661607553 - 2²⁵ = 1628053121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1661607559) 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, 10516425 + ... + 10516582.

It is an arithmetic number, because the mean of its divisors is an integer number (420660160).

Almost surely, 2^1661607553 is an apocalyptic number.

It is an amenable number.

1661607553 is a deficient number, since it is larger than the sum of its proper divisors (21033087).

1661607553 is an equidigital number, since it uses as much as digits as its factorization.

1661607553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21033086.

The product of its (nonzero) digits is 113400, while the sum is 40.

The square root of 1661607553 is about 40762.8207193761. The cubic root of 1661607553 is about 1184.4302371121.

The spelling of 1661607553 in words is "one billion, six hundred sixty-one million, six hundred seven thousand, five hundred fifty-three".