81103721 has 2 divisors, whose sum is σ = 81103722. Its totient is φ = 81103720.

The previous prime is 81103619. The next prime is 81103733. The reversal of 81103721 is 12730118.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 46717225 + 34386496 = 6835^2 + 5864^2 .

It is a cyclic number.

It is not a de Polignac number, because 81103721 - 2¹⁴ = 81087337 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (81103751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40551860 + 40551861.

It is an arithmetic number, because the mean of its divisors is an integer number (40551861).

Almost surely, 2^81103721 is an apocalyptic number.

It is an amenable number.

81103721 is a deficient number, since it is larger than the sum of its proper divisors (1).

81103721 is an equidigital number, since it uses as much as digits as its factorization.

81103721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 336, while the sum is 23.

The square root of 81103721 is about 9005.7604342998. The cubic root of 81103721 is about 432.8594732676.

Adding to 81103721 its reverse (12730118), we get a palindrome (93833839).

The spelling of 81103721 in words is "eighty-one million, one hundred three thousand, seven hundred twenty-one".