639951 has 16 divisors (see below), whose sum is σ = 937440. Its totient is φ = 385920.

The previous prime is 639949. The next prime is 639959. The reversal of 639951 is 159936.

It is not a de Polignac number, because 639951 - 2¹ = 639949 is a prime.

It is an Ulam number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 639951.

It is not an unprimeable number, because it can be changed into a prime (639959) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2245 + ... + 2513.

It is an arithmetic number, because the mean of its divisors is an integer number (58590).

2⁶³⁹⁹⁵¹ is an apocalyptic number.

639951 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

639951 is a deficient number, since it is larger than the sum of its proper divisors (297489).

639951 is a wasteful number, since it uses less digits than its factorization.

639951 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 346.

The product of its digits is 7290, while the sum is 33.

The square root of 639951 is about 799.9693744138. The cubic root of 639951 is about 86.1751882264.

The spelling of 639951 in words is "six hundred thirty-nine thousand, nine hundred fifty-one".