81509393 has 6 divisors (see below), whose sum is σ = 94817106. Its totient is φ = 69865152.

The previous prime is 81509387. The next prime is 81509413. The reversal of 81509393 is 39390518.

It can be written as a sum of positive squares in only one way, i.e., 81414529 + 94864 = 9023^2 + 308^2 .

It is not a de Polignac number, because 81509393 - 2¹² = 81505297 is a prime.

It is a super-2 number, since 2×81509393² = 13287562294456898, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81509303) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 831680 + ... + 831777.

It is an arithmetic number, because the mean of its divisors is an integer number (15802851).

Almost surely, 2^81509393 is an apocalyptic number.

It is an amenable number.

81509393 is a deficient number, since it is larger than the sum of its proper divisors (13307713).

81509393 is a wasteful number, since it uses less digits than its factorization.

81509393 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1663471 (or 1663464 counting only the distinct ones).

The product of its (nonzero) digits is 29160, while the sum is 38.

The square root of 81509393 is about 9028.2552578004. The cubic root of 81509393 is about 433.5799786538.

The spelling of 81509393 in words is "eighty-one million, five hundred nine thousand, three hundred ninety-three".