81557923 has 2 divisors, whose sum is σ = 81557924. Its totient is φ = 81557922.

The previous prime is 81557921. The next prime is 81557933. The reversal of 81557923 is 32975518.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81557923 - 2¹ = 81557921 is a prime.

Together with 81557921, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81557921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40778961 + 40778962.

It is an arithmetic number, because the mean of its divisors is an integer number (40778962).

Almost surely, 2^81557923 is an apocalyptic number.

81557923 is a deficient number, since it is larger than the sum of its proper divisors (1).

81557923 is an equidigital number, since it uses as much as digits as its factorization.

81557923 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 75600, while the sum is 40.

The square root of 81557923 is about 9030.9425310983. The cubic root of 81557923 is about 433.6660115267. Note that the first 3 decimals are identical.

The spelling of 81557923 in words is "eighty-one million, five hundred fifty-seven thousand, nine hundred twenty-three".