638708981 has 4 divisors (see below), whose sum is σ = 638759712. Its totient is φ = 638658252.

The previous prime is 638708977. The next prime is 638709041. The reversal of 638708981 is 189807836.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 638708981 - 2² = 638708977 is a prime.

It is a super-2 number, since 2×638708981² = 815898324820116722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638708381) 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, 9440 + ... + 36966.

It is an arithmetic number, because the mean of its divisors is an integer number (159689928).

Almost surely, 2^638708981 is an apocalyptic number.

It is an amenable number.

638708981 is a deficient number, since it is larger than the sum of its proper divisors (50731).

638708981 is a wasteful number, since it uses less digits than its factorization.

638708981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50730.

The product of its (nonzero) digits is 580608, while the sum is 50.

The square root of 638708981 is about 25272.6923971309. The cubic root of 638708981 is about 861.1940242507.

The spelling of 638708981 in words is "six hundred thirty-eight million, seven hundred eight thousand, nine hundred eighty-one".