63998991 has 40 divisors (see below), whose sum is σ = 111966624. Its totient is φ = 35665920.

The previous prime is 63998981. The next prime is 63999017. The reversal of 63998991 is 19989936.

It is not a de Polignac number, because 63998991 - 2⁵ = 63998959 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (63998941) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 21871 + ... + 24623.

Almost surely, 2^63998991 is an apocalyptic number.

63998991 is a deficient number, since it is larger than the sum of its proper divisors (47967633).

63998991 is a wasteful number, since it uses less digits than its factorization.

63998991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2813 (or 2804 counting only the distinct ones).

The product of its digits is 944784, while the sum is 54.

The square root of 63998991 is about 7999.9369372514. The cubic root of 63998991 is about 399.9978979056.

The spelling of 63998991 in words is "sixty-three million, nine hundred ninety-eight thousand, nine hundred ninety-one".