81273781 has 4 divisors (see below), whose sum is σ = 81993132. Its totient is φ = 80554432.

The previous prime is 81273761. The next prime is 81273799. The reversal of 81273781 is 18737218.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 18737218 = 2 ⋅9368609.

It can be written as a sum of positive squares in 2 ways, for example, as 10562500 + 70711281 = 3250^2 + 8409^2 .

It is a cyclic number.

It is not a de Polignac number, because 81273781 - 2⁷ = 81273653 is a prime.

It is a super-2 number, since 2×81273781² = 13210854956071922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 81273781.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81273701) 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, 359506 + ... + 359731.

It is an arithmetic number, because the mean of its divisors is an integer number (20498283).

Almost surely, 2^81273781 is an apocalyptic number.

It is an amenable number.

81273781 is a deficient number, since it is larger than the sum of its proper divisors (719351).

81273781 is a wasteful number, since it uses less digits than its factorization.

81273781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 719350.

The product of its digits is 18816, while the sum is 37.

The square root of 81273781 is about 9015.1972246868. The cubic root of 81273781 is about 433.1618050247.

The spelling of 81273781 in words is "eighty-one million, two hundred seventy-three thousand, seven hundred eighty-one".