81939569 has 2 divisors, whose sum is σ = 81939570. Its totient is φ = 81939568.

The previous prime is 81939503. The next prime is 81939601. The reversal of 81939569 is 96593918.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 80013025 + 1926544 = 8945^2 + 1388^2 .

It is a cyclic number.

It is not a de Polignac number, because 81939569 - 2⁸ = 81939313 is a prime.

It is a super-2 number, since 2×81939569² = 13428185935811522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81929569) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40969784 + 40969785.

It is an arithmetic number, because the mean of its divisors is an integer number (40969785).

Almost surely, 2^81939569 is an apocalyptic number.

It is an amenable number.

81939569 is a deficient number, since it is larger than the sum of its proper divisors (1).

81939569 is an equidigital number, since it uses as much as digits as its factorization.

81939569 is an evil number, because the sum of its binary digits is even.

The product of its digits is 524880, while the sum is 50.

The square root of 81939569 is about 9052.0477793701. The cubic root of 81939569 is about 434.3413982185.

The spelling of 81939569 in words is "eighty-one million, nine hundred thirty-nine thousand, five hundred sixty-nine".