81766021 has 4 divisors (see below), whose sum is σ = 81862732. Its totient is φ = 81669312.

The previous prime is 81766019. The next prime is 81766031. The reversal of 81766021 is 12066718.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 5832225 + 75933796 = 2415^2 + 8714^2 .

It is a cyclic number.

It is not a de Polignac number, because 81766021 - 2¹ = 81766019 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 (81766001) 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, 47076 + ... + 48781.

It is an arithmetic number, because the mean of its divisors is an integer number (20465683).

Almost surely, 2^81766021 is an apocalyptic number.

It is an amenable number.

81766021 is a deficient number, since it is larger than the sum of its proper divisors (96711).

81766021 is an equidigital number, since it uses as much as digits as its factorization.

81766021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 96710.

The product of its (nonzero) digits is 4032, while the sum is 31.

The square root of 81766021 is about 9042.4565799345. The cubic root of 81766021 is about 434.0345364575.

The spelling of 81766021 in words is "eighty-one million, seven hundred sixty-six thousand, twenty-one".