81721361 has 2 divisors, whose sum is σ = 81721362. Its totient is φ = 81721360.

The previous prime is 81721331. The next prime is 81721373. The reversal of 81721361 is 16312718.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 58140625 + 23580736 = 7625^2 + 4856^2 .

It is a cyclic number.

It is not a de Polignac number, because 81721361 - 2²⁶ = 14612497 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81721331) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40860680 + 40860681.

It is an arithmetic number, because the mean of its divisors is an integer number (40860681).

Almost surely, 2^81721361 is an apocalyptic number.

It is an amenable number.

81721361 is a deficient number, since it is larger than the sum of its proper divisors (1).

81721361 is an equidigital number, since it uses as much as digits as its factorization.

81721361 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2016, while the sum is 29.

The square root of 81721361 is about 9039.9867809638. The cubic root of 81721361 is about 433.9554999076.

The spelling of 81721361 in words is "eighty-one million, seven hundred twenty-one thousand, three hundred sixty-one".