691531 has 2 divisors, whose sum is σ = 691532. Its totient is φ = 691530.

The previous prime is 691499. The next prime is 691553. The reversal of 691531 is 135196.

691531 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 is a cyclic number.

It is not a de Polignac number, because 691531 - 2⁵ = 691499 is a prime.

It is a super-2 number, since 2×691531² = 956430247922, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 691496 and 691505.

It is not a weakly prime, because it can be changed into another prime (691591) by changing a digit.

It is a good prime.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 345765 + 345766.

It is an arithmetic number, because the mean of its divisors is an integer number (345766).

2⁶⁹¹⁵³¹ is an apocalyptic number.

691531 is the 445-th centered heptagonal number.

691531 is a deficient number, since it is larger than the sum of its proper divisors (1).

691531 is an equidigital number, since it uses as much as digits as its factorization.

691531 is an evil number, because the sum of its binary digits is even.

The product of its digits is 810, while the sum is 25.

The square root of 691531 is about 831.5834293683. The cubic root of 691531 is about 88.4308673080.

It can be divided in two parts, 69 and 1531, that added together give a square (1600 = 40²).

The spelling of 691531 in words is "six hundred ninety-one thousand, five hundred thirty-one".