21240253 has 2 divisors, whose sum is σ = 21240254. Its totient is φ = 21240252.

The previous prime is 21240251. The next prime is 21240283. The reversal of 21240253 is 35204212.

It is the 1882-nd star number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17656804 + 3583449 = 4202^2 + 1893^2 .

It is a cyclic number.

It is not a de Polignac number, because 21240253 - 2¹ = 21240251 is a prime.

It is a super-2 number, since 2×21240253² = 902296695008018, which contains 22 as substring.

Together with 21240251, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21240253.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21240251) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10620126 + 10620127.

It is an arithmetic number, because the mean of its divisors is an integer number (10620127).

Almost surely, 2^21240253 is an apocalyptic number.

It is an amenable number.

21240253 is a deficient number, since it is larger than the sum of its proper divisors (1).

21240253 is an equidigital number, since it uses as much as digits as its factorization.

21240253 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 480, while the sum is 19.

The square root of 21240253 is about 4608.7148968015. The cubic root of 21240253 is about 276.9405573031.

Adding to 21240253 its reverse (35204212), we get a palindrome (56444465).

The spelling of 21240253 in words is "twenty-one million, two hundred forty thousand, two hundred fifty-three".