81209719 has 4 divisors (see below), whose sum is σ = 81288040. Its totient is φ = 81131400.

The previous prime is 81209717. The next prime is 81209747. The reversal of 81209719 is 91790218.

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 81209719 - 2¹ = 81209717 is a prime.

It is a super-2 number, since 2×81209719² = 13190036920117922, 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 (81209717) 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, 37584 + ... + 39685.

It is an arithmetic number, because the mean of its divisors is an integer number (20322010).

Almost surely, 2^81209719 is an apocalyptic number.

81209719 is a deficient number, since it is larger than the sum of its proper divisors (78321).

81209719 is a wasteful number, since it uses less digits than its factorization.

81209719 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 78320.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 81209719 is about 9011.6435237974. The cubic root of 81209719 is about 433.0479655007.

The spelling of 81209719 in words is "eighty-one million, two hundred nine thousand, seven hundred nineteen".