81907639 has 4 divisors (see below), whose sum is σ = 89353800. Its totient is φ = 74461480.

The previous prime is 81907633. The next prime is 81907643. The reversal of 81907639 is 93670918.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81907639 - 2⁵ = 81907607 is a prime.

It is a super-2 number, since 2×81907639² = 13417722653108642, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81907595 and 81907604.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81907633) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3723064 + ... + 3723085.

It is an arithmetic number, because the mean of its divisors is an integer number (22338450).

Almost surely, 2^81907639 is an apocalyptic number.

81907639 is a deficient number, since it is larger than the sum of its proper divisors (7446161).

81907639 is a wasteful number, since it uses less digits than its factorization.

81907639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7446160.

The product of its (nonzero) digits is 81648, while the sum is 43.

The square root of 81907639 is about 9050.2839181984. The cubic root of 81907639 is about 434.2849732099.

The spelling of 81907639 in words is "eighty-one million, nine hundred seven thousand, six hundred thirty-nine".