691151621 has 2 divisors, whose sum is σ = 691151622. Its totient is φ = 691151620.

The previous prime is 691151597. The next prime is 691151623. The reversal of 691151621 is 126151196.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 567630625 + 123520996 = 23825^2 + 11114^2 .

It is a cyclic number.

It is not a de Polignac number, because 691151621 - 2¹⁰ = 691150597 is a prime.

Together with 691151623, 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 (691151623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345575810 + 345575811.

It is an arithmetic number, because the mean of its divisors is an integer number (345575811).

Almost surely, 2^691151621 is an apocalyptic number.

It is an amenable number.

691151621 is a deficient number, since it is larger than the sum of its proper divisors (1).

691151621 is an equidigital number, since it uses as much as digits as its factorization.

691151621 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3240, while the sum is 32.

The square root of 691151621 is about 26289.7626653418. The cubic root of 691151621 is about 884.1469307480.

The spelling of 691151621 in words is "six hundred ninety-one million, one hundred fifty-one thousand, six hundred twenty-one".