81381761 has 4 divisors (see below), whose sum is σ = 83366724. Its totient is φ = 79396800.

The previous prime is 81381733. The next prime is 81381779. The reversal of 81381761 is 16718318.

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 10080625 + 71301136 = 3175^2 + 8444^2 .

It is a cyclic number.

It is not a de Polignac number, because 81381761 - 2⁶ = 81381697 is a prime.

It is a super-2 number, since 2×81381761² = 13245982046922242, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81381701) 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, 992420 + ... + 992501.

It is an arithmetic number, because the mean of its divisors is an integer number (20841681).

Almost surely, 2^81381761 is an apocalyptic number.

It is an amenable number.

81381761 is a deficient number, since it is larger than the sum of its proper divisors (1984963).

81381761 is a wasteful number, since it uses less digits than its factorization.

81381761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1984962.

The product of its digits is 8064, while the sum is 35.

The square root of 81381761 is about 9021.1840131992. The cubic root of 81381761 is about 433.3535524425.

The spelling of 81381761 in words is "eighty-one million, three hundred eighty-one thousand, seven hundred sixty-one".