81249913 has 2 divisors, whose sum is σ = 81249914. Its totient is φ = 81249912.

The previous prime is 81249911. The next prime is 81249923. The reversal of 81249913 is 31994218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 52606009 + 28643904 = 7253^2 + 5352^2 .

It is a cyclic number.

It is not a de Polignac number, because 81249913 - 2¹ = 81249911 is a prime.

Together with 81249911, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (81249911) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40624956 + 40624957.

It is an arithmetic number, because the mean of its divisors is an integer number (40624957).

Almost surely, 2^81249913 is an apocalyptic number.

It is an amenable number.

81249913 is a deficient number, since it is larger than the sum of its proper divisors (1).

81249913 is an equidigital number, since it uses as much as digits as its factorization.

81249913 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 37.

The square root of 81249913 is about 9013.8733627670. The cubic root of 81249913 is about 433.1193980800.

The spelling of 81249913 in words is "eighty-one million, two hundred forty-nine thousand, nine hundred thirteen".