686971781 has 2 divisors, whose sum is σ = 686971782. Its totient is φ = 686971780.

The previous prime is 686971763. The next prime is 686971783. The reversal of 686971781 is 187179686.

686971781 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 598780900 + 88190881 = 24470^2 + 9391^2 .

It is a cyclic number.

It is not a de Polignac number, because 686971781 - 2¹⁸ = 686709637 is a prime.

It is a super-2 number, since 2×686971781² = 943860455780623922, which contains 22 as substring.

Together with 686971783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (686971783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343485890 + 343485891.

It is an arithmetic number, because the mean of its divisors is an integer number (343485891).

Almost surely, 2^686971781 is an apocalyptic number.

It is an amenable number.

686971781 is a deficient number, since it is larger than the sum of its proper divisors (1).

686971781 is an equidigital number, since it uses as much as digits as its factorization.

686971781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1016064, while the sum is 53.

The square root of 686971781 is about 26210.1465276331. The cubic root of 686971781 is about 882.3609899094.

The spelling of 686971781 in words is "six hundred eighty-six million, nine hundred seventy-one thousand, seven hundred eighty-one".