21002081 has 2 divisors, whose sum is σ = 21002082. Its totient is φ = 21002080.

The previous prime is 21002077. The next prime is 21002083. The reversal of 21002081 is 18020012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11669056 + 9333025 = 3416^2 + 3055^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002081 - 2² = 21002077 is a prime.

It is a super-2 number, since 2×21002081² = 882174812661122, which contains 22 as substring.

Together with 21002083, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21002083) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501040 + 10501041.

It is an arithmetic number, because the mean of its divisors is an integer number (10501041).

Almost surely, 2^21002081 is an apocalyptic number.

It is an amenable number.

21002081 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002081 is an equidigital number, since it uses as much as digits as its factorization.

21002081 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 21002081 is about 4582.8027450459. The cubic root of 21002081 is about 275.9015305454.

Adding to 21002081 its reverse (18020012), we get a palindrome (39022093).

The spelling of 21002081 in words is "twenty-one million, two thousand, eighty-one".