665219978 has 4 divisors (see below), whose sum is σ = 997829970. Its totient is φ = 332609988.

The previous prime is 665219923. The next prime is 665219993. The reversal of 665219978 is 879912566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 445083409 + 220136569 = 21097^2 + 14837^2 .

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 166304993 + ... + 166304996.

Almost surely, 2^665219978 is an apocalyptic number.

665219978 is a deficient number, since it is larger than the sum of its proper divisors (332609992).

665219978 is a wasteful number, since it uses less digits than its factorization.

665219978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 332609991.

The product of its digits is 1632960, while the sum is 53.

The square root of 665219978 is about 25791.8587542659. The cubic root of 665219978 is about 872.9481076247.

The spelling of 665219978 in words is "six hundred sixty-five million, two hundred nineteen thousand, nine hundred seventy-eight".