21080021 has 2 divisors, whose sum is σ = 21080022. Its totient is φ = 21080020.

The previous prime is 21079999. The next prime is 21080041. The reversal of 21080021 is 12008012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20295025 + 784996 = 4505^2 + 886^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21080021 is a prime.

It is a super-3 number, since 3×21080021³ (a number of 23 digits) contains 333 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21079978 and 21080005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21080041) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10540010 + 10540011.

It is an arithmetic number, because the mean of its divisors is an integer number (10540011).

Almost surely, 2^21080021 is an apocalyptic number.

It is an amenable number.

21080021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21080021 is an equidigital number, since it uses as much as digits as its factorization.

21080021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 32, while the sum is 14.

The square root of 21080021 is about 4591.2984002349. The cubic root of 21080021 is about 276.2424050108.

Adding to 21080021 its reverse (12008012), we get a palindrome (33088033).

It can be divided in two parts, 210800 and 21, that multiplied together give a triangular number (4426800 = T₂₉₇₅).

The spelling of 21080021 in words is "twenty-one million, eighty thousand, twenty-one".