81690689 has 2 divisors, whose sum is σ = 81690690. Its totient is φ = 81690688.

The previous prime is 81690659. The next prime is 81690691. The reversal of 81690689 is 98609618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81306289 + 384400 = 9017^2 + 620^2 .

It is a cyclic number.

It is not a de Polignac number, because 81690689 - 2¹⁶ = 81625153 is a prime.

Together with 81690691, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (81690619) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40845344 + 40845345.

It is an arithmetic number, because the mean of its divisors is an integer number (40845345).

Almost surely, 2^81690689 is an apocalyptic number.

It is an amenable number.

81690689 is a deficient number, since it is larger than the sum of its proper divisors (1).

81690689 is an equidigital number, since it uses as much as digits as its factorization.

81690689 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 186624, while the sum is 47.

The square root of 81690689 is about 9038.2901590954. The cubic root of 81690689 is about 433.9012017882.

The spelling of 81690689 in words is "eighty-one million, six hundred ninety thousand, six hundred eighty-nine".