686717021 has 4 divisors (see below), whose sum is σ = 691729692. Its totient is φ = 681704352.

The previous prime is 686716997. The next prime is 686717081. The reversal of 686717021 is 120717686.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 571927225 + 114789796 = 23915^2 + 10714^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-686717021 is a prime.

It is a super-2 number, since 2×686717021² = 943160533862228882, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (686717081) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2506130 + ... + 2506403.

It is an arithmetic number, because the mean of its divisors is an integer number (172932423).

Almost surely, 2^686717021 is an apocalyptic number.

It is an amenable number.

686717021 is a deficient number, since it is larger than the sum of its proper divisors (5012671).

686717021 is a wasteful number, since it uses less digits than its factorization.

686717021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5012670.

The product of its (nonzero) digits is 28224, while the sum is 38.

The square root of 686717021 is about 26205.2861270393. The cubic root of 686717021 is about 882.2519033913.

The spelling of 686717021 in words is "six hundred eighty-six million, seven hundred seventeen thousand, twenty-one".