81566919 has 30 divisors (see below), whose sum is σ = 141747144. Its totient is φ = 46607400.

The previous prime is 81566909. The next prime is 81566941. The reversal of 81566919 is 91966518.

81566919 is a `hidden beast` number, since 81 + 566 + 9 + 1 + 9 = 666.

It is not a de Polignac number, because 81566919 - 2¹⁵ = 81534151 is a prime.

It is a super-2 number, since 2×81566919² = 13306324550305122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81566909) by changing a digit.

It is a polite number, since it can be written in 29 ways as a sum of consecutive naturals, for example, 6307 + ... + 14244.

Almost surely, 2^81566919 is an apocalyptic number.

81566919 is a deficient number, since it is larger than the sum of its proper divisors (60180225).

81566919 is a wasteful number, since it uses less digits than its factorization.

81566919 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20577 (or 20561 counting only the distinct ones).

The product of its digits is 116640, while the sum is 45.

The square root of 81566919 is about 9031.4405827642. The cubic root of 81566919 is about 433.6819556797.

The spelling of 81566919 in words is "eighty-one million, five hundred sixty-six thousand, nine hundred nineteen".