81721369 has 8 divisors (see below), whose sum is σ = 85440960. Its totient is φ = 78015696.

The previous prime is 81721361. The next prime is 81721373. The reversal of 81721369 is 96312718.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 81721369 - 2³ = 81721361 is a prime.

It is a super-2 number, since 2×81721369² = 13356764302468322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81721361) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9622 + ... + 16000.

It is an arithmetic number, because the mean of its divisors is an integer number (10680120).

Almost surely, 2^81721369 is an apocalyptic number.

It is an amenable number.

81721369 is a deficient number, since it is larger than the sum of its proper divisors (3719591).

81721369 is a wasteful number, since it uses less digits than its factorization.

81721369 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6959.

The product of its digits is 18144, while the sum is 37.

The square root of 81721369 is about 9039.9872234423. The cubic root of 81721369 is about 433.9555140681.

The spelling of 81721369 in words is "eighty-one million, seven hundred twenty-one thousand, three hundred sixty-nine".