81902721 has 4 divisors (see below), whose sum is σ = 109203632. Its totient is φ = 54601812.

The previous prime is 81902693. The next prime is 81902729. The reversal of 81902721 is 12720918.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 81902721 - 2⁷ = 81902593 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (81902729) 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, 13650451 + ... + 13650456.

It is an arithmetic number, because the mean of its divisors is an integer number (27300908).

Almost surely, 2^81902721 is an apocalyptic number.

It is an amenable number.

81902721 is a deficient number, since it is larger than the sum of its proper divisors (27300911).

81902721 is a wasteful number, since it uses less digits than its factorization.

81902721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27300910.

The product of its (nonzero) digits is 2016, while the sum is 30.

The square root of 81902721 is about 9050.0122099365. The cubic root of 81902721 is about 434.2762810770.

The spelling of 81902721 in words is "eighty-one million, nine hundred two thousand, seven hundred twenty-one".