81566549 has 4 divisors (see below), whose sum is σ = 84197760. Its totient is φ = 78935340.

The previous prime is 81566539. The next prime is 81566567. The reversal of 81566549 is 94566518.

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: 94566518 = 2 ⋅47283259.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81566549 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 (81566509) 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, 1315559 + ... + 1315620.

It is an arithmetic number, because the mean of its divisors is an integer number (21049440).

Almost surely, 2^81566549 is an apocalyptic number.

It is an amenable number.

81566549 is a deficient number, since it is larger than the sum of its proper divisors (2631211).

81566549 is a wasteful number, since it uses less digits than its factorization.

81566549 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2631210.

The product of its digits is 259200, while the sum is 44.

The square root of 81566549 is about 9031.4200987442. The cubic root of 81566549 is about 433.6812999295.

The spelling of 81566549 in words is "eighty-one million, five hundred sixty-six thousand, five hundred forty-nine".