638953981 has 4 divisors (see below), whose sum is σ = 639695232. Its totient is φ = 638212732.

The previous prime is 638953979. The next prime is 638954033. The reversal of 638953981 is 189359836.

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.

It is a cyclic number.

It is not a de Polignac number, because 638953981 - 2¹ = 638953979 is a prime.

It is a super-2 number, since 2×638953981² = 816524379671496722, 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 (638953951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 369331 + ... + 371056.

It is an arithmetic number, because the mean of its divisors is an integer number (159923808).

Almost surely, 2^638953981 is an apocalyptic number.

It is an amenable number.

638953981 is a deficient number, since it is larger than the sum of its proper divisors (741251).

638953981 is an equidigital number, since it uses as much as digits as its factorization.

638953981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 741250.

The product of its digits is 1399680, while the sum is 52.

The square root of 638953981 is about 25277.5390613881. The cubic root of 638953981 is about 861.3041242441.

It can be divided in two parts, 63895 and 3981, that added together give a palindrome (67876).

The spelling of 638953981 in words is "six hundred thirty-eight million, nine hundred fifty-three thousand, nine hundred eighty-one".