665656421 has 4 divisors (see below), whose sum is σ = 669105612. Its totient is φ = 662207232.

The previous prime is 665656399. The next prime is 665656423. The reversal of 665656421 is 124656566.

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 81902500 + 583753921 = 9050^2 + 24161^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-665656421 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665656423) 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, 1724306 + ... + 1724691.

It is an arithmetic number, because the mean of its divisors is an integer number (167276403).

Almost surely, 2^665656421 is an apocalyptic number.

It is an amenable number.

665656421 is a deficient number, since it is larger than the sum of its proper divisors (3449191).

665656421 is a wasteful number, since it uses less digits than its factorization.

665656421 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3449190.

The product of its digits is 259200, while the sum is 41.

The square root of 665656421 is about 25800.3182344715. The cubic root of 665656421 is about 873.1389762157.

The spelling of 665656421 in words is "six hundred sixty-five million, six hundred fifty-six thousand, four hundred twenty-one".