81656189 has 2 divisors, whose sum is σ = 81656190. Its totient is φ = 81656188.

The previous prime is 81656149. The next prime is 81656191. The reversal of 81656189 is 98165618.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 81631225 + 24964 = 9035^2 + 158^2 .

It is a cyclic number.

It is not a de Polignac number, because 81656189 - 2¹⁶ = 81590653 is a prime.

It is a super-3 number, since 3×81656189³ (a number of 25 digits) contains 333 as substring.

It is a Sophie Germain prime.

Together with 81656191, it forms a pair of twin primes.

It is a Chen prime.

It is an alternating number because its digits alternate between even and odd.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81656149) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40828094 + 40828095.

It is an arithmetic number, because the mean of its divisors is an integer number (40828095).

Almost surely, 2^81656189 is an apocalyptic number.

It is an amenable number.

81656189 is a deficient number, since it is larger than the sum of its proper divisors (1).

81656189 is an equidigital number, since it uses as much as digits as its factorization.

81656189 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 103680, while the sum is 44.

The square root of 81656189 is about 9036.3814107197. The cubic root of 81656189 is about 433.8401107814.

The spelling of 81656189 in words is "eighty-one million, six hundred fifty-six thousand, one hundred eighty-nine".