81911457 has 24 divisors (see below), whose sum is σ = 129603240. Its totient is φ = 49620480.

The previous prime is 81911443. The next prime is 81911461. The reversal of 81911457 is 75411918.

It can be written as a sum of positive squares in 4 ways, for example, as 5803281 + 76108176 = 2409^2 + 8724^2 .

It is not a de Polignac number, because 81911457 - 2⁸ = 81911201 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81911407) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 4794 + ... + 13667.

It is an arithmetic number, because the mean of its divisors is an integer number (5400135).

Almost surely, 2^81911457 is an apocalyptic number.

81911457 is a gapful number since it is divisible by the number (87) formed by its first and last digit.

It is an amenable number.

81911457 is a deficient number, since it is larger than the sum of its proper divisors (47691783).

81911457 is a wasteful number, since it uses less digits than its factorization.

81911457 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18513 (or 18510 counting only the distinct ones).

The product of its digits is 10080, while the sum is 36.

The square root of 81911457 is about 9050.4948483495. The cubic root of 81911457 is about 434.2917209496.

The spelling of 81911457 in words is "eighty-one million, nine hundred eleven thousand, four hundred fifty-seven".