21210100081 has 2 divisors, whose sum is σ = 21210100082. Its totient is φ = 21210100080.

The previous prime is 21210100057. The next prime is 21210100111. The reversal of 21210100081 is 18000101212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20148383025 + 1061717056 = 141945^2 + 32584^2 .

It is a cyclic number.

It is not a de Polignac number, because 21210100081 - 2⁹ = 21210099569 is a prime.

It is a super-2 number, since 2×21210100081² (a number of 21 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21210100481) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10605050040 + 10605050041.

It is an arithmetic number, because the mean of its divisors is an integer number (10605050041).

Almost surely, 2^21210100081 is an apocalyptic number.

It is an amenable number.

21210100081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21210100081 is an equidigital number, since it uses as much as digits as its factorization.

21210100081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32, while the sum is 16.

Adding to 21210100081 its reverse (18000101212), we get a palindrome (39210201293).

The spelling of 21210100081 in words is "twenty-one billion, two hundred ten million, one hundred thousand, eighty-one".