81506709 has 16 divisors (see below), whose sum is σ = 120926400. Its totient is φ = 54258768.

The previous prime is 81506693. The next prime is 81506771. The reversal of 81506709 is 90760518.

81506709 is a `hidden beast` number, since 81 + 506 + 70 + 9 = 666.

It is not a de Polignac number, because 81506709 - 2⁴ = 81506693 is a prime.

It is a super-2 number, since 2×81506709² = 13286687224021362, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81506609) 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, 21262 + ... + 24800.

It is an arithmetic number, because the mean of its divisors is an integer number (7557900).

Almost surely, 2^81506709 is an apocalyptic number.

It is an amenable number.

81506709 is a deficient number, since it is larger than the sum of its proper divisors (39419691).

81506709 is a wasteful number, since it uses less digits than its factorization.

81506709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4401 (or 4395 counting only the distinct ones).

The product of its (nonzero) digits is 15120, while the sum is 36.

The square root of 81506709 is about 9028.1066121308. The cubic root of 81506709 is about 433.5752195236.

It can be divided in two parts, 81506 and 709, that added together give a triangular number (82215 = T₄₀₅).

The spelling of 81506709 in words is "eighty-one million, five hundred six thousand, seven hundred nine".