81125781 has 20 divisors (see below), whose sum is σ = 119048160. Its totient is φ = 49140520.

The previous prime is 81125771. The next prime is 81125797. The reversal of 81125781 is 18752118.

It is not a de Polignac number, because 81125781 - 2⁵ = 81125749 is a prime.

It is a super-2 number, since 2×81125781² = 13162784685719922, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (33).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81125701) by changing a digit.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 43000 + ... + 44846.

It is an arithmetic number, because the mean of its divisors is an integer number (5952408).

Almost surely, 2^81125781 is an apocalyptic number.

It is an amenable number.

81125781 is a deficient number, since it is larger than the sum of its proper divisors (37922379).

81125781 is an equidigital number, since it uses as much as digits as its factorization.

81125781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1894 (or 1861 counting only the distinct ones).

The product of its digits is 4480, while the sum is 33.

The square root of 81125781 is about 9006.9851226701. The cubic root of 81125781 is about 432.8987152582.

Adding to 81125781 its reverse (18752118), we get a palindrome (99877899).

The spelling of 81125781 in words is "eighty-one million, one hundred twenty-five thousand, seven hundred eighty-one".