21002521 has 2 divisors, whose sum is σ = 21002522. Its totient is φ = 21002520.

The previous prime is 21002507. The next prime is 21002539. The reversal of 21002521 is 12520012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10634121 + 10368400 = 3261^2 + 3220^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002521 - 2⁷ = 21002393 is a prime.

It is a super-2 number, since 2×21002521² = 882211776710882, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21002591) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10501260 + 10501261.

It is an arithmetic number, because the mean of its divisors is an integer number (10501261).

Almost surely, 2^21002521 is an apocalyptic number.

It is an amenable number.

21002521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002521 is an equidigital number, since it uses as much as digits as its factorization.

21002521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 40, while the sum is 13.

The square root of 21002521 is about 4582.8507503518. The cubic root of 21002521 is about 275.9034572723.

Adding to 21002521 its reverse (12520012), we get a palindrome (33522533).

The spelling of 21002521 in words is "twenty-one million, two thousand, five hundred twenty-one".