66561553 has 4 divisors (see below), whose sum is σ = 67652788. Its totient is φ = 65470320.

The previous prime is 66561527. The next prime is 66561569. The reversal of 66561553 is 35516566.

It is a happy number.

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 16265089 + 50296464 = 4033^2 + 7092^2 .

It is a cyclic number.

It is not a de Polignac number, because 66561553 - 2⁹ = 66561041 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66568553) 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, 545526 + ... + 545647.

It is an arithmetic number, because the mean of its divisors is an integer number (16913197).

Almost surely, 2^66561553 is an apocalyptic number.

It is an amenable number.

66561553 is a deficient number, since it is larger than the sum of its proper divisors (1091235).

66561553 is a wasteful number, since it uses less digits than its factorization.

66561553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1091234.

The product of its digits is 81000, while the sum is 37.

The square root of 66561553 is about 8158.5263988051. The cubic root of 66561553 is about 405.2669134197.

The spelling of 66561553 in words is "sixty-six million, five hundred sixty-one thousand, five hundred fifty-three".