691216681 has 9 divisors (see below), whose sum is σ = 704368119. Its totient is φ = 678307800.

The previous prime is 691216667. The next prime is 691216697. The reversal of 691216681 is 186612196.

The square root of 691216681 is 26291.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 22477081 + 668739600 = 4741^2 + 25860^2 .

It is not a de Polignac number, because 691216681 - 2¹⁷ = 691085609 is a prime.

It is a super-2 number, since 2×691216681² = 955561000185311522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (691216621) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 1603536 + ... + 1603966.

Almost surely, 2^691216681 is an apocalyptic number.

691216681 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

691216681 is the 26291-st square number.

691216681 is the 13146-th centered octagonal number.

It is an amenable number.

691216681 is a deficient number, since it is larger than the sum of its proper divisors (13151438).

691216681 is an frugal number, since it uses more digits than its factorization.

691216681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 984 (or 492 counting only the distinct ones).

The product of its digits is 31104, while the sum is 40.

The cubic root of 691216681 is about 884.1746722703.

The spelling of 691216681 in words is "six hundred ninety-one million, two hundred sixteen thousand, six hundred eighty-one".