691959981621 has 4 divisors (see below), whose sum is σ = 922613308832. Its totient is φ = 461306654412.

The previous prime is 691959981613. The next prime is 691959981623. The reversal of 691959981621 is 126189959196.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 691959981621 - 2³ = 691959981613 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (691959981623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 115326663601 + ... + 115326663606.

It is an arithmetic number, because the mean of its divisors is an integer number (230653327208).

Almost surely, 2^691959981621 is an apocalyptic number.

It is an amenable number.

691959981621 is a deficient number, since it is larger than the sum of its proper divisors (230653327211).

691959981621 is a wasteful number, since it uses less digits than its factorization.

691959981621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 230653327210.

The product of its digits is 18895680, while the sum is 66.

The spelling of 691959981621 in words is "six hundred ninety-one billion, nine hundred fifty-nine million, nine hundred eighty-one thousand, six hundred twenty-one".