81507893 has 4 divisors (see below), whose sum is σ = 84318540. Its totient is φ = 78697248.

The previous prime is 81507889. The next prime is 81507901. The reversal of 81507893 is 39870518.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 39870518 = 2 ⋅19935259.

It can be written as a sum of positive squares in 2 ways, for example, as 50794129 + 30713764 = 7127^2 + 5542^2 .

It is a cyclic number.

It is not a de Polignac number, because 81507893 - 2² = 81507889 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81507893.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81507863) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1405280 + ... + 1405337.

It is an arithmetic number, because the mean of its divisors is an integer number (21079635).

Almost surely, 2^81507893 is an apocalyptic number.

It is an amenable number.

81507893 is a deficient number, since it is larger than the sum of its proper divisors (2810647).

81507893 is a wasteful number, since it uses less digits than its factorization.

81507893 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2810646.

The product of its (nonzero) digits is 60480, while the sum is 41.

The square root of 81507893 is about 9028.1721848888. The cubic root of 81507893 is about 433.5773189442.

Subtracting from 81507893 its reverse (39870518), we obtain a triangular number (41637375 = T₉₁₂₅).

The spelling of 81507893 in words is "eighty-one million, five hundred seven thousand, eight hundred ninety-three".