663891637 has 4 divisors (see below), whose sum is σ = 664020396. Its totient is φ = 663762880.

The previous prime is 663891607. The next prime is 663891643. The reversal of 663891637 is 736198366.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 736198366 = 2 ⋅368099183.

It can be written as a sum of positive squares in 2 ways, for example, as 397842916 + 266048721 = 19946^2 + 16311^2 .

It is a cyclic number.

It is not a de Polignac number, because 663891637 - 2¹⁵ = 663858869 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 (663891607) 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, 56308 + ... + 67069.

It is an arithmetic number, because the mean of its divisors is an integer number (166005099).

Almost surely, 2^663891637 is an apocalyptic number.

It is an amenable number.

663891637 is a deficient number, since it is larger than the sum of its proper divisors (128759).

663891637 is a wasteful number, since it uses less digits than its factorization.

663891637 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 128758.

The product of its digits is 979776, while the sum is 49.

The square root of 663891637 is about 25766.0947176711. The cubic root of 663891637 is about 872.3666731685.

The spelling of 663891637 in words is "six hundred sixty-three million, eight hundred ninety-one thousand, six hundred thirty-seven".