81557933 has 2 divisors, whose sum is σ = 81557934. Its totient is φ = 81557932.

The previous prime is 81557923. The next prime is 81557939. The reversal of 81557933 is 33975518.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 57957769 + 23600164 = 7613^2 + 4858^2 .

It is a cyclic number.

It is not a de Polignac number, because 81557933 - 2⁸ = 81557677 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81557939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40778966 + 40778967.

It is an arithmetic number, because the mean of its divisors is an integer number (40778967).

Almost surely, 2^81557933 is an apocalyptic number.

It is an amenable number.

81557933 is a deficient number, since it is larger than the sum of its proper divisors (1).

81557933 is an equidigital number, since it uses as much as digits as its factorization.

81557933 is an evil number, because the sum of its binary digits is even.

The product of its digits is 113400, while the sum is 41.

The square root of 81557933 is about 9030.9430847503. The cubic root of 81557933 is about 433.6660292510. Note that the first 3 decimals are identical.

The spelling of 81557933 in words is "eighty-one million, five hundred fifty-seven thousand, nine hundred thirty-three".