638631 has 32 divisors (see below), whose sum is σ = 1126400. Its totient is φ = 349920.

The previous prime is 638629. The next prime is 638633. The reversal of 638631 is 136836.

It is an interprime number because it is at equal distance from previous prime (638629) and next prime (638633).

It is not a de Polignac number, because 638631 - 2¹ = 638629 is a prime.

It is a super-2 number, since 2×638631² = 815699108322, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

638631 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 638595 and 638604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 5805 + ... + 5913.

It is an arithmetic number, because the mean of its divisors is an integer number (35200).

2⁶³⁸⁶³¹ is an apocalyptic number.

638631 is a deficient number, since it is larger than the sum of its proper divisors (487769).

638631 is a wasteful number, since it uses less digits than its factorization.

638631 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 156 (or 150 counting only the distinct ones).

The product of its digits is 2592, while the sum is 27.

The square root of 638631 is about 799.1439169511. The cubic root of 638631 is about 86.1158974639.

638631 divided by its sum of digits (27) gives a triangular number (23653 = T₂₁₇).

The spelling of 638631 in words is "six hundred thirty-eight thousand, six hundred thirty-one".