81512781 has 16 divisors (see below), whose sum is σ = 126555264. Its totient is φ = 45699264.

The previous prime is 81512777. The next prime is 81512833. The reversal of 81512781 is 18721518.

It is not a de Polignac number, because 81512781 - 2² = 81512777 is a prime.

It is a super-2 number, since 2×81512781² = 13288666932707922, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81512731) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 35506 + ... + 37731.

It is an arithmetic number, because the mean of its divisors is an integer number (7909704).

Almost surely, 2^81512781 is an apocalyptic number.

It is an amenable number.

81512781 is a deficient number, since it is larger than the sum of its proper divisors (45042483).

81512781 is a wasteful number, since it uses less digits than its factorization.

81512781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 73300.

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

The square root of 81512781 is about 9028.4428890036. The cubic root of 81512781 is about 433.5859859313.

The spelling of 81512781 in words is "eighty-one million, five hundred twelve thousand, seven hundred eighty-one".