66561657 has 4 divisors (see below), whose sum is σ = 88748880. Its totient is φ = 44374436.

The previous prime is 66561637. The next prime is 66561659. The reversal of 66561657 is 75616566.

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.

It is a cyclic number.

It is not a de Polignac number, because 66561657 - 2¹⁴ = 66545273 is a prime.

It is not an unprimeable number, because it can be changed into a prime (66561659) 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, 11093607 + ... + 11093612.

It is an arithmetic number, because the mean of its divisors is an integer number (22187220).

Almost surely, 2^66561657 is an apocalyptic number.

It is an amenable number.

66561657 is a deficient number, since it is larger than the sum of its proper divisors (22187223).

66561657 is a wasteful number, since it uses less digits than its factorization.

66561657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22187222.

The product of its digits is 226800, while the sum is 42.

The square root of 66561657 is about 8158.5327725027. The cubic root of 66561657 is about 405.2671244912.

The spelling of 66561657 in words is "sixty-six million, five hundred sixty-one thousand, six hundred fifty-seven".