81909645 has 32 divisors (see below), whose sum is σ = 134462592. Its totient is φ = 42561792.

The previous prime is 81909623. The next prime is 81909679. The reversal of 81909645 is 54690918.

It is not a de Polignac number, because 81909645 - 2⁸ = 81909389 is a prime.

It is a super-3 number, since 3×81909645³ (a number of 25 digits) contains 333 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81909597 and 81909606.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 156354 + ... + 156876.

It is an arithmetic number, because the mean of its divisors is an integer number (4201956).

Almost surely, 2^81909645 is an apocalyptic number.

It is an amenable number.

81909645 is a deficient number, since it is larger than the sum of its proper divisors (52552947).

81909645 is a wasteful number, since it uses less digits than its factorization.

81909645 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 781.

The product of its (nonzero) digits is 77760, while the sum is 42.

The square root of 81909645 is about 9050.3947427723. The cubic root of 81909645 is about 434.2885185388.

The spelling of 81909645 in words is "eighty-one million, nine hundred nine thousand, six hundred forty-five".