81651973 has 8 divisors (see below), whose sum is σ = 88013016. Its totient is φ = 75302400.

The previous prime is 81651971. The next prime is 81651979. The reversal of 81651973 is 37915618.

It can be written as a sum of positive squares in 4 ways, for example, as 18258529 + 63393444 = 4273^2 + 7962^2 .

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 81651973 - 2¹ = 81651971 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81651971) 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, 17133 + ... + 21373.

It is an arithmetic number, because the mean of its divisors is an integer number (11001627).

Almost surely, 2^81651973 is an apocalyptic number.

It is an amenable number.

81651973 is a deficient number, since it is larger than the sum of its proper divisors (6361043).

81651973 is a wasteful number, since it uses less digits than its factorization.

81651973 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5735.

The product of its digits is 45360, while the sum is 40.

The square root of 81651973 is about 9036.1481284893. The cubic root of 81651973 is about 433.8326441035.

The spelling of 81651973 in words is "eighty-one million, six hundred fifty-one thousand, nine hundred seventy-three".