81551 has 2 divisors, whose sum is σ = 81552. Its totient is φ = 81550.

The previous prime is 81547. The next prime is 81553. The reversal of 81551 is 15518.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81551 - 2² = 81547 is a prime.

Together with 81553, it forms a pair of twin primes.

It is a Chen prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81553) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40775 + 40776.

It is an arithmetic number, because the mean of its divisors is an integer number (40776).

2⁸¹⁵⁵¹ is an apocalyptic number.

81551 is a deficient number, since it is larger than the sum of its proper divisors (1).

81551 is an equidigital number, since it uses as much as digits as its factorization.

81551 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 200, while the sum is 20.

The square root of 81551 is about 285.5713571071. The cubic root of 81551 is about 43.3653740678.

The spelling of 81551 in words is "eighty-one thousand, five hundred fifty-one".