766663991 has 4 divisors (see below), whose sum is σ = 799997232. Its totient is φ = 733330752.

The previous prime is 766663987. The next prime is 766664021. The reversal of 766663991 is 199366667.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199366667 = 17 ⋅11727451.

It is a cyclic number.

It is not a de Polignac number, because 766663991 - 2² = 766663987 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 (766663901) 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, 16666586 + ... + 16666631.

It is an arithmetic number, because the mean of its divisors is an integer number (199999308).

Almost surely, 2^766663991 is an apocalyptic number.

766663991 is a deficient number, since it is larger than the sum of its proper divisors (33333241).

766663991 is a wasteful number, since it uses less digits than its factorization.

766663991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 33333240.

The product of its digits is 2204496, while the sum is 53.

The square root of 766663991 is about 27688.6978928226. The cubic root of 766663991 is about 915.2400620273.

The spelling of 766663991 in words is "seven hundred sixty-six million, six hundred sixty-three thousand, nine hundred ninety-one".