81139787 has 4 divisors (see below), whose sum is σ = 82051560. Its totient is φ = 80228016.

The previous prime is 81139781. The next prime is 81139811. The reversal of 81139787 is 78793118.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 78793118 = 2 ⋅39396559.

It is a cyclic number.

It is not a de Polignac number, because 81139787 - 2¹⁴ = 81123403 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81139781) 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, 455753 + ... + 455930.

It is an arithmetic number, because the mean of its divisors is an integer number (20512890).

Almost surely, 2^81139787 is an apocalyptic number.

81139787 is a deficient number, since it is larger than the sum of its proper divisors (911773).

81139787 is an equidigital number, since it uses as much as digits as its factorization.

81139787 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 911772.

The product of its digits is 84672, while the sum is 44.

The square root of 81139787 is about 9007.7625967828. The cubic root of 81139787 is about 432.9236264945.

The spelling of 81139787 in words is "eighty-one million, one hundred thirty-nine thousand, seven hundred eighty-seven".