81980721 has 16 divisors (see below), whose sum is σ = 122161920. Its totient is φ = 54334800.

The previous prime is 81980719. The next prime is 81980741. The reversal of 81980721 is 12708918.

It is not a de Polignac number, because 81980721 - 2¹ = 81980719 is a prime.

It is a plaindrome in base 12.

It is not an unprimeable number, because it can be changed into a prime (81980741) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4105 + ... + 13446.

It is an arithmetic number, because the mean of its divisors is an integer number (7635120).

Almost surely, 2^81980721 is an apocalyptic number.

It is an amenable number.

81980721 is a deficient number, since it is larger than the sum of its proper divisors (40181199).

81980721 is a wasteful number, since it uses less digits than its factorization.

81980721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 17733 (or 17727 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 81980721 is about 9054.3205708656. The cubic root of 81980721 is about 434.4140982421.

The spelling of 81980721 in words is "eighty-one million, nine hundred eighty thousand, seven hundred twenty-one".