661643553 has 16 divisors (see below), whose sum is σ = 974699136. Its totient is φ = 397098240.

The previous prime is 661643539. The next prime is 661643579. The reversal of 661643553 is 355346166.

It is a happy number.

It is not a de Polignac number, because 661643553 - 2²² = 657449249 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (661643503) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 280858 + ... + 283203.

It is an arithmetic number, because the mean of its divisors is an integer number (60918696).

Almost surely, 2^661643553 is an apocalyptic number.

It is an amenable number.

661643553 is a deficient number, since it is larger than the sum of its proper divisors (313055583).

661643553 is a wasteful number, since it uses less digits than its factorization.

661643553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 564104.

The product of its digits is 194400, while the sum is 39.

The square root of 661643553 is about 25722.4328748274. The cubic root of 661643553 is about 871.3808840940.

The spelling of 661643553 in words is "six hundred sixty-one million, six hundred forty-three thousand, five hundred fifty-three".