81721841 has 2 divisors, whose sum is σ = 81721842. Its totient is φ = 81721840.

The previous prime is 81721819. The next prime is 81721867. The reversal of 81721841 is 14812718.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 49561600 + 32160241 = 7040^2 + 5671^2 .

It is a cyclic number.

It is not a de Polignac number, because 81721841 - 2¹⁴ = 81705457 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 81721798 and 81721807.

It is not a weakly prime, because it can be changed into another prime (81721811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40860920 + 40860921.

It is an arithmetic number, because the mean of its divisors is an integer number (40860921).

Almost surely, 2^81721841 is an apocalyptic number.

It is an amenable number.

81721841 is a deficient number, since it is larger than the sum of its proper divisors (1).

81721841 is an equidigital number, since it uses as much as digits as its factorization.

81721841 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3584, while the sum is 32.

The square root of 81721841 is about 9040.0133296362. The cubic root of 81721841 is about 433.9563495355.

The spelling of 81721841 in words is "eighty-one million, seven hundred twenty-one thousand, eight hundred forty-one".