691020020209 has 2 divisors, whose sum is σ = 691020020210. Its totient is φ = 691020020208.

The previous prime is 691020020191. The next prime is 691020020219. The reversal of 691020020209 is 902020020196.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 633337430625 + 57682589584 = 795825^2 + 240172^2 .

It is a cyclic number.

It is not a de Polignac number, because 691020020209 - 2¹⁹ = 691019495921 is a prime.

It is not a weakly prime, because it can be changed into another prime (691020020219) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345510010104 + 345510010105.

It is an arithmetic number, because the mean of its divisors is an integer number (345510010105).

Almost surely, 2^691020020209 is an apocalyptic number.

It is an amenable number.

691020020209 is a deficient number, since it is larger than the sum of its proper divisors (1).

691020020209 is an equidigital number, since it uses as much as digits as its factorization.

691020020209 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3888, while the sum is 31.

The spelling of 691020020209 in words is "six hundred ninety-one billion, twenty million, twenty thousand, two hundred nine".