688137981 has 8 divisors (see below), whose sum is σ = 918732384. Its totient is φ = 458151120.

The previous prime is 688137979. The next prime is 688137997. The reversal of 688137981 is 189731886.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 688137981 - 2¹ = 688137979 is a prime.

It is a super-2 number, since 2×688137981² = 947067761789512722, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (688137941) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 149235 + ... + 153776.

It is an arithmetic number, because the mean of its divisors is an integer number (114841548).

Almost surely, 2^688137981 is an apocalyptic number.

It is an amenable number.

688137981 is a deficient number, since it is larger than the sum of its proper divisors (230594403).

688137981 is a wasteful number, since it uses less digits than its factorization.

688137981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 303771.

The product of its digits is 580608, while the sum is 51.

The square root of 688137981 is about 26232.3842034993. The cubic root of 688137981 is about 882.8600049019.

The spelling of 688137981 in words is "six hundred eighty-eight million, one hundred thirty-seven thousand, nine hundred eighty-one".