21012281 has 2 divisors, whose sum is σ = 21012282. Its totient is φ = 21012280.

The previous prime is 21012259. The next prime is 21012283. The reversal of 21012281 is 18221012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20839225 + 173056 = 4565^2 + 416^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21012281 is a prime.

It is a super-2 number, since 2×21012281² = 883031905645922, which contains 22 as substring.

Together with 21012283, 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 (21012283) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506140 + 10506141.

It is an arithmetic number, because the mean of its divisors is an integer number (10506141).

Almost surely, 2^21012281 is an apocalyptic number.

It is an amenable number.

21012281 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012281 is an equidigital number, since it uses as much as digits as its factorization.

21012281 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 64, while the sum is 17.

The square root of 21012281 is about 4583.9154660617. The cubic root of 21012281 is about 275.9461886620.

Adding to 21012281 its reverse (18221012), we get a palindrome (39233293).

The spelling of 21012281 in words is "twenty-one million, twelve thousand, two hundred eighty-one".