691906 has 4 divisors (see below), whose sum is σ = 1037862. Its totient is φ = 345952.

The previous prime is 691903. The next prime is 691907. The reversal of 691906 is 609196.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 502681 + 189225 = 709^2 + 435^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an Ulam number.

It is not an unprimeable number, because it can be changed into a prime (691903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 172975 + ... + 172978.

2⁶⁹¹⁹⁰⁶ is an apocalyptic number.

691906 is a deficient number, since it is larger than the sum of its proper divisors (345956).

691906 is a wasteful number, since it uses less digits than its factorization.

691906 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 345955.

The product of its (nonzero) digits is 2916, while the sum is 31.

The square root of 691906 is about 831.8088722778. The cubic root of 691906 is about 88.4468490368.

It can be divided in two parts, 69190 and 6, that added together give a palindrome (69196).

The spelling of 691906 in words is "six hundred ninety-one thousand, nine hundred six".