81531617 has 4 divisors (see below), whose sum is σ = 81747120. Its totient is φ = 81316116.

The previous prime is 81531601. The next prime is 81531623. The reversal of 81531617 is 71613518.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 71613518 = 2 ⋅35806759.

It is a cyclic number.

It is not a de Polignac number, because 81531617 - 2⁴ = 81531601 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81531517) 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, 107183 + ... + 107940.

It is an arithmetic number, because the mean of its divisors is an integer number (20436780).

Almost surely, 2^81531617 is an apocalyptic number.

It is an amenable number.

81531617 is a deficient number, since it is larger than the sum of its proper divisors (215503).

81531617 is a wasteful number, since it uses less digits than its factorization.

81531617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 215502.

The product of its digits is 5040, while the sum is 32.

The square root of 81531617 is about 9029.4859765105. The cubic root of 81531617 is about 433.6193810894.

The spelling of 81531617 in words is "eighty-one million, five hundred thirty-one thousand, six hundred seventeen".