81908691 has 8 divisors (see below), whose sum is σ = 111272400. Its totient is φ = 53575392.

The previous prime is 81908689. The next prime is 81908699. The reversal of 81908691 is 19680918.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 81908691 - 2¹ = 81908689 is a prime.

It is a super-2 number, since 2×81908691² = 13418067322666962, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81908699) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 257416 + ... + 257733.

It is an arithmetic number, because the mean of its divisors is an integer number (13909050).

Almost surely, 2^81908691 is an apocalyptic number.

81908691 is a deficient number, since it is larger than the sum of its proper divisors (29363709).

81908691 is a wasteful number, since it uses less digits than its factorization.

81908691 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 515205.

The product of its (nonzero) digits is 31104, while the sum is 42.

The square root of 81908691 is about 9050.3420377354. The cubic root of 81908691 is about 434.2868324823.

The spelling of 81908691 in words is "eighty-one million, nine hundred eight thousand, six hundred ninety-one".