665409621 has 16 divisors (see below), whose sum is σ = 943544000. Its totient is φ = 415922688.

The previous prime is 665409617. The next prime is 665409707. The reversal of 665409621 is 126904566.

665409621 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 665409621 - 2² = 665409617 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 665409621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665409601) 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, 54646 + ... + 65703.

It is an arithmetic number, because the mean of its divisors is an integer number (58971500).

Almost surely, 2^665409621 is an apocalyptic number.

It is an amenable number.

665409621 is a deficient number, since it is larger than the sum of its proper divisors (278134379).

665409621 is a wasteful number, since it uses less digits than its factorization.

665409621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 120468.

The product of its (nonzero) digits is 77760, while the sum is 39.

The square root of 665409621 is about 25795.5349043202. The cubic root of 665409621 is about 873.0310540054.

The spelling of 665409621 in words is "six hundred sixty-five million, four hundred nine thousand, six hundred twenty-one".