81149721 has 32 divisors (see below), whose sum is σ = 117936000. Its totient is φ = 49443840.

The previous prime is 81149711. The next prime is 81149749. The reversal of 81149721 is 12794118.

It is not a de Polignac number, because 81149721 - 2¹⁵ = 81116953 is a prime.

It is not an unprimeable number, because it can be changed into a prime (81149711) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 448251 + ... + 448431.

It is an arithmetic number, because the mean of its divisors is an integer number (3685500).

Almost surely, 2^81149721 is an apocalyptic number.

It is an amenable number.

81149721 is a deficient number, since it is larger than the sum of its proper divisors (36786279).

81149721 is a wasteful number, since it uses less digits than its factorization.

81149721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 409.

The product of its digits is 4032, while the sum is 33.

The square root of 81149721 is about 9008.3139931954. The cubic root of 81149721 is about 432.9412934861.

The spelling of 81149721 in words is "eighty-one million, one hundred forty-nine thousand, seven hundred twenty-one".