81461591 has 4 divisors (see below), whose sum is σ = 81485184. Its totient is φ = 81438000.

The previous prime is 81461581. The next prime is 81461659. The reversal of 81461591 is 19516418.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19516418 = 2 ⋅9758209.

It is a cyclic number.

It is not a de Polignac number, because 81461591 - 2¹⁴ = 81445207 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81461581) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5495 + ... + 13896.

It is an arithmetic number, because the mean of its divisors is an integer number (20371296).

Almost surely, 2^81461591 is an apocalyptic number.

81461591 is a deficient number, since it is larger than the sum of its proper divisors (23593).

81461591 is a wasteful number, since it uses less digits than its factorization.

81461591 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23592.

The product of its digits is 8640, while the sum is 35.

The square root of 81461591 is about 9025.6075141788. The cubic root of 81461591 is about 433.4952029719.

The spelling of 81461591 in words is "eighty-one million, four hundred sixty-one thousand, five hundred ninety-one".