21001000100081 has 2 divisors, whose sum is σ = 21001000100082. Its totient is φ = 21001000100080.

The previous prime is 21001000100057. The next prime is 21001000100107. The reversal of 21001000100081 is 18000100010012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19787017027600 + 1213983072481 = 4448260^2 + 1101809^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001000100081 - 2³⁸ = 20726122193137 is a prime.

It is a super-2 number, since 2×21001000100081² (a number of 27 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21001000105081) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500500050040 + 10500500050041.

It is an arithmetic number, because the mean of its divisors is an integer number (10500500050041).

Almost surely, 2^{21001000100081} is an apocalyptic number.

It is an amenable number.

21001000100081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001000100081 is an equidigital number, since it uses as much as digits as its factorization.

21001000100081 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 16, while the sum is 14.

Adding to 21001000100081 its reverse (18000100010012), we get a palindrome (39001100110093).

The spelling of 21001000100081 in words is "twenty-one trillion, one billion, one hundred thousand, eighty-one".