81721370 has 8 divisors (see below), whose sum is σ = 147098484. Its totient is φ = 32688544.

The previous prime is 81721361. The next prime is 81721373. The reversal of 81721370 is 7312718.

It can be written as a sum of positive squares in 2 ways, for example, as 81558961 + 162409 = 9031^2 + 403^2 .

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

It is not an unprimeable number, because it can be changed into a prime (81721373) 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, 4086059 + ... + 4086078.

Almost surely, 2^81721370 is an apocalyptic number.

81721370 is a deficient number, since it is larger than the sum of its proper divisors (65377114).

81721370 is a wasteful number, since it uses less digits than its factorization.

81721370 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8172144.

The product of its (nonzero) digits is 2352, while the sum is 29.

The square root of 81721370 is about 9039.9872787521. The cubic root of 81721370 is about 433.9555158382.

The spelling of 81721370 in words is "eighty-one million, seven hundred twenty-one thousand, three hundred seventy".