688491938 has 4 divisors (see below), whose sum is σ = 1032737910. Its totient is φ = 344245968.

The previous prime is 688491931. The next prime is 688491977. The reversal of 688491938 is 839194886.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 839194886 = 2 ⋅419597443.

It can be written as a sum of positive squares in only one way, i.e., 676884289 + 11607649 = 26017^2 + 3407^2 .

It is a super-2 number, since 2×688491938² = 948042297381991688, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (688491931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 172122983 + ... + 172122986.

Almost surely, 2^688491938 is an apocalyptic number.

688491938 is a deficient number, since it is larger than the sum of its proper divisors (344245972).

688491938 is a wasteful number, since it uses less digits than its factorization.

688491938 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 344245971.

The product of its digits is 2985984, while the sum is 56.

The square root of 688491938 is about 26239.1299017326. The cubic root of 688491938 is about 883.0113509612.

The spelling of 688491938 in words is "six hundred eighty-eight million, four hundred ninety-one thousand, nine hundred thirty-eight".