665556121 has 4 divisors (see below), whose sum is σ = 665665744. Its totient is φ = 665446500.

The previous prime is 665556113. The next prime is 665556131. The reversal of 665556121 is 121655566.

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 665556121 - 2³ = 665556113 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665556131) 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, 45135 + ... + 58036.

It is an arithmetic number, because the mean of its divisors is an integer number (166416436).

Almost surely, 2^665556121 is an apocalyptic number.

It is an amenable number.

665556121 is a deficient number, since it is larger than the sum of its proper divisors (109623).

665556121 is a wasteful number, since it uses less digits than its factorization.

665556121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109622.

The product of its digits is 54000, while the sum is 37.

The square root of 665556121 is about 25798.3743867710. The cubic root of 665556121 is about 873.0951196377.

The spelling of 665556121 in words is "six hundred sixty-five million, five hundred fifty-six thousand, one hundred twenty-one".