638661309 has 64 divisors (see below), whose sum is σ = 1052835840. Its totient is φ = 340866240.

The previous prime is 638661301. The next prime is 638661311. The reversal of 638661309 is 903166836.

It is not a de Polignac number, because 638661309 - 2³ = 638661301 is a prime.

It is a super-2 number, since 2×638661309² = 815776535227186962, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (638661301) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 1667332 + ... + 1667714.

It is an arithmetic number, because the mean of its divisors is an integer number (16450560).

Almost surely, 2^638661309 is an apocalyptic number.

638661309 is a gapful number since it is divisible by the number (69) formed by its first and last digit.

It is an amenable number.

638661309 is a deficient number, since it is larger than the sum of its proper divisors (414174531).

638661309 is a wasteful number, since it uses less digits than its factorization.

638661309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 459 (or 433 counting only the distinct ones).

The product of its (nonzero) digits is 139968, while the sum is 42.

The square root of 638661309 is about 25271.7492271509. The cubic root of 638661309 is about 861.1725977668.

The spelling of 638661309 in words is "six hundred thirty-eight million, six hundred sixty-one thousand, three hundred nine".