665999401 has 4 divisors (see below), whose sum is σ = 666055252. Its totient is φ = 665943552.

The previous prime is 665999377. The next prime is 665999407. The reversal of 665999401 is 104999566.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 201640000 + 464359401 = 14200^2 + 21549^2 .

It is a cyclic number.

It is not a de Polignac number, because 665999401 - 2⁷ = 665999273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665999407) 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, 2040 + ... + 36553.

It is an arithmetic number, because the mean of its divisors is an integer number (166513813).

Almost surely, 2^665999401 is an apocalyptic number.

It is an amenable number.

665999401 is a deficient number, since it is larger than the sum of its proper divisors (55851).

665999401 is a wasteful number, since it uses less digits than its factorization.

665999401 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 55850.

The product of its (nonzero) digits is 524880, while the sum is 49.

The square root of 665999401 is about 25806.9641957360. The cubic root of 665999401 is about 873.2889123176.

The spelling of 665999401 in words is "six hundred sixty-five million, nine hundred ninety-nine thousand, four hundred one".