81559813 has 2 divisors, whose sum is σ = 81559814. Its totient is φ = 81559812.

The previous prime is 81559811. The next prime is 81559843. The reversal of 81559813 is 31895518.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 79977249 + 1582564 = 8943^2 + 1258^2 .

It is a cyclic number.

It is not a de Polignac number, because 81559813 - 2¹ = 81559811 is a prime.

It is a super-4 number, since 4×81559813⁴ (a number of 33 digits) contains 4444 as substring.

Together with 81559811, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81559811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40779906 + 40779907.

It is an arithmetic number, because the mean of its divisors is an integer number (40779907).

Almost surely, 2^81559813 is an apocalyptic number.

It is an amenable number.

81559813 is a deficient number, since it is larger than the sum of its proper divisors (1).

81559813 is an equidigital number, since it uses as much as digits as its factorization.

81559813 is an evil number, because the sum of its binary digits is even.

The product of its digits is 43200, while the sum is 40.

The square root of 81559813 is about 9031.0471707327. The cubic root of 81559813 is about 433.6693613849.

The spelling of 81559813 in words is "eighty-one million, five hundred fifty-nine thousand, eight hundred thirteen".