81947309 has 4 divisors (see below), whose sum is σ = 82072320. Its totient is φ = 81822300.

The previous prime is 81947297. The next prime is 81947329. The reversal of 81947309 is 90374918.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-81947309 is a prime.

It is a super-2 number, since 2×81947309² = 13430722904682962, 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 (81947329) 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, 61517 + ... + 62834.

It is an arithmetic number, because the mean of its divisors is an integer number (20518080).

Almost surely, 2^81947309 is an apocalyptic number.

It is an amenable number.

81947309 is a deficient number, since it is larger than the sum of its proper divisors (125011).

81947309 is a wasteful number, since it uses less digits than its factorization.

81947309 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 125010.

The product of its (nonzero) digits is 54432, while the sum is 41.

The square root of 81947309 is about 9052.4752968456. The cubic root of 81947309 is about 434.3550737301.

The spelling of 81947309 in words is "eighty-one million, nine hundred forty-seven thousand, three hundred nine".