691521217 has 2 divisors, whose sum is σ = 691521218. Its totient is φ = 691521216.

The previous prime is 691521203. The next prime is 691521221. The reversal of 691521217 is 712125196.

691521217 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., 480661776 + 210859441 = 21924^2 + 14521^2 .

It is a cyclic number.

It is not a de Polignac number, because 691521217 - 2²³ = 683132609 is a prime.

It is a super-2 number, since 2×691521217² = 956403187122322178, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (691521277) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345760608 + 345760609.

It is an arithmetic number, because the mean of its divisors is an integer number (345760609).

Almost surely, 2^691521217 is an apocalyptic number.

It is an amenable number.

691521217 is a deficient number, since it is larger than the sum of its proper divisors (1).

691521217 is an equidigital number, since it uses as much as digits as its factorization.

691521217 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7560, while the sum is 34.

The square root of 691521217 is about 26296.7910019455. The cubic root of 691521217 is about 884.3045029931.

The spelling of 691521217 in words is "six hundred ninety-one million, five hundred twenty-one thousand, two hundred seventeen".