638623440 has 720 divisors, whose sum is σ = 2889065088. Its totient is φ = 127650816.

The previous prime is 638623429. The next prime is 638623483. The reversal of 638623440 is 44326836.

638623440 = T₁₀₉ + T₁₁₀ + ... + T₁₅₆₄.

It is a happy number.

638623440 is a `hidden beast` number, since 6 + 386 + 234 + 40 = 666.

It is a Cunningham number, because it is equal to 25271²-1.

It is a tau number, because it is divible by the number of its divisors (720).

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a junction number, because it is equal to n+sod(n) for n = 638623395 and 638623404.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 143 ways as a sum of consecutive naturals, for example, 33611751 + ... + 33611769.

Almost surely, 2^638623440 is an apocalyptic number.

638623440 is a gapful number since it is divisible by the number (60) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 638623440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1444532544).

638623440 is an abundant number, since it is smaller than the sum of its proper divisors (2250441648).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

638623440 is a wasteful number, since it uses less digits than its factorization.

638623440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 86 (or 49 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 36.

The square root of 638623440 is about 25270.9999802145. Note that the first 4 decimals coincide. The cubic root of 638623440 is about 861.1555765438.

The spelling of 638623440 in words is "six hundred thirty-eight million, six hundred twenty-three thousand, four hundred forty".