81209101 has 2 divisors, whose sum is σ = 81209102. Its totient is φ = 81209100.

The previous prime is 81209099. The next prime is 81209111. The reversal of 81209101 is 10190218.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 78322500 + 2886601 = 8850^2 + 1699^2 .

It is a cyclic number.

It is not a de Polignac number, because 81209101 - 2¹ = 81209099 is a prime.

Together with 81209099, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81209111) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40604550 + 40604551.

It is an arithmetic number, because the mean of its divisors is an integer number (40604551).

Almost surely, 2^81209101 is an apocalyptic number.

It is an amenable number.

81209101 is a deficient number, since it is larger than the sum of its proper divisors (1).

81209101 is an equidigital number, since it uses as much as digits as its factorization.

81209101 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 144, while the sum is 22.

The square root of 81209101 is about 9011.6092347594. The cubic root of 81209101 is about 433.0468670102.

Adding to 81209101 its reverse (10190218), we get a palindrome (91399319).

The spelling of 81209101 in words is "eighty-one million, two hundred nine thousand, one hundred one".