81209779 has 8 divisors (see below), whose sum is σ = 92870240. Its totient is φ = 69564096.

The previous prime is 81209767. The next prime is 81209797. The reversal of 81209779 is 97790218.

It is a happy number.

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

It is not a de Polignac number, because 81209779 - 2⁵ = 81209747 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (81209759) 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, 13327 + ... + 18439.

It is an arithmetic number, because the mean of its divisors is an integer number (11608780).

Almost surely, 2^81209779 is an apocalyptic number.

81209779 is a deficient number, since it is larger than the sum of its proper divisors (11660461).

81209779 is a wasteful number, since it uses less digits than its factorization.

81209779 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7389.

The product of its (nonzero) digits is 63504, while the sum is 43.

The square root of 81209779 is about 9011.6468528233. The cubic root of 81209779 is about 433.0480721500.

The spelling of 81209779 in words is "eighty-one million, two hundred nine thousand, seven hundred seventy-nine".