684720209 has 2 divisors, whose sum is σ = 684720210. Its totient is φ = 684720208.

The previous prime is 684720199. The next prime is 684720229. The reversal of 684720209 is 902027486.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 676000000 + 8720209 = 26000^2 + 2953^2 .

It is a cyclic number.

It is not a de Polignac number, because 684720209 - 2²⁸ = 416284753 is a prime.

It is a super-2 number, since 2×684720209² = 937683529226007362, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (684720229) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 342360104 + 342360105.

It is an arithmetic number, because the mean of its divisors is an integer number (342360105).

Almost surely, 2^684720209 is an apocalyptic number.

It is an amenable number.

684720209 is a deficient number, since it is larger than the sum of its proper divisors (1).

684720209 is an equidigital number, since it uses as much as digits as its factorization.

684720209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48384, while the sum is 38.

The square root of 684720209 is about 26167.1589783836. The cubic root of 684720209 is about 881.3959460242.

The spelling of 684720209 in words is "six hundred eighty-four million, seven hundred twenty thousand, two hundred nine".