81689669 has 2 divisors, whose sum is σ = 81689670. Its totient is φ = 81689668.

The previous prime is 81689653. The next prime is 81689677. The reversal of 81689669 is 96698618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81685444 + 4225 = 9038^2 + 65^2 .

It is a cyclic number.

It is not a de Polignac number, because 81689669 - 2⁴ = 81689653 is a prime.

It is a super-2 number, since 2×81689669² = 13346404042659122, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 81689669.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81689269) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40844834 + 40844835.

It is an arithmetic number, because the mean of its divisors is an integer number (40844835).

Almost surely, 2^81689669 is an apocalyptic number.

It is an amenable number.

81689669 is a deficient number, since it is larger than the sum of its proper divisors (1).

81689669 is an equidigital number, since it uses as much as digits as its factorization.

81689669 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1119744, while the sum is 53.

The square root of 81689669 is about 9038.2337323174. The cubic root of 81689669 is about 433.8993958660.

The spelling of 81689669 in words is "eighty-one million, six hundred eighty-nine thousand, six hundred sixty-nine".