81406639 has 4 divisors (see below), whose sum is σ = 81447840. Its totient is φ = 81365440.

The previous prime is 81406627. The next prime is 81406643. The reversal of 81406639 is 93660418.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 93660418 = 2 ⋅46830209.

It is a cyclic number.

It is not a de Polignac number, because 81406639 - 2¹¹ = 81404591 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 81406598 and 81406607.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81406939) 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, 17479 + ... + 21640.

It is an arithmetic number, because the mean of its divisors is an integer number (20361960).

Almost surely, 2^81406639 is an apocalyptic number.

81406639 is a deficient number, since it is larger than the sum of its proper divisors (41201).

81406639 is a wasteful number, since it uses less digits than its factorization.

81406639 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 41200.

The product of its (nonzero) digits is 31104, while the sum is 37.

The square root of 81406639 is about 9022.5627734031. The cubic root of 81406639 is about 433.3977059529.

The spelling of 81406639 in words is "eighty-one million, four hundred six thousand, six hundred thirty-nine".