81985913 has 2 divisors, whose sum is σ = 81985914. Its totient is φ = 81985912.

The previous prime is 81985889. The next prime is 81985921. The reversal of 81985913 is 31958918.

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., 76090729 + 5895184 = 8723^2 + 2428^2 .

It is a cyclic number.

It is not a de Polignac number, because 81985913 - 2¹² = 81981817 is a prime.

It is not a weakly prime, because it can be changed into another prime (81985933) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40992956 + 40992957.

It is an arithmetic number, because the mean of its divisors is an integer number (40992957).

Almost surely, 2^81985913 is an apocalyptic number.

It is an amenable number.

81985913 is a deficient number, since it is larger than the sum of its proper divisors (1).

81985913 is an equidigital number, since it uses as much as digits as its factorization.

81985913 is an evil number, because the sum of its binary digits is even.

The product of its digits is 77760, while the sum is 44.

The square root of 81985913 is about 9054.6072802745. The cubic root of 81985913 is about 434.4232688144.

The spelling of 81985913 in words is "eighty-one million, nine hundred eighty-five thousand, nine hundred thirteen".