81309071 has 4 divisors (see below), whose sum is σ = 84844272. Its totient is φ = 77773872.

The previous prime is 81309047. The next prime is 81309073. The reversal of 81309071 is 17090318.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81309071 - 2²² = 77114767 is a prime.

It is a super-2 number, since 2×81309071² = 13222330053766082, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81309073) 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, 1767566 + ... + 1767611.

It is an arithmetic number, because the mean of its divisors is an integer number (21211068).

Almost surely, 2^81309071 is an apocalyptic number.

81309071 is a deficient number, since it is larger than the sum of its proper divisors (3535201).

81309071 is a wasteful number, since it uses less digits than its factorization.

81309071 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3535200.

The product of its (nonzero) digits is 1512, while the sum is 29.

The square root of 81309071 is about 9017.1542628481. The cubic root of 81309071 is about 433.2244905466.

Adding to 81309071 its reverse (17090318), we get a palindrome (98399389).

The spelling of 81309071 in words is "eighty-one million, three hundred nine thousand, seventy-one".