21642253 has 4 divisors (see below), whose sum is σ = 21662208. Its totient is φ = 21622300.

The previous prime is 21642239. The next prime is 21642259. The reversal of 21642253 is 35224612.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21642253 is a prime.

It is a super-2 number, since 2×21642253² = 936774229832018, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21642259) 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 in 3 ways as a sum of consecutive naturals, for example, 8251 + ... + 10552.

It is an arithmetic number, because the mean of its divisors is an integer number (5415552).

Almost surely, 2^21642253 is an apocalyptic number.

It is an amenable number.

21642253 is a deficient number, since it is larger than the sum of its proper divisors (19955).

21642253 is a wasteful number, since it uses less digits than its factorization.

21642253 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 19954.

The product of its digits is 2880, while the sum is 25.

The square root of 21642253 is about 4652.1234936317. The cubic root of 21642253 is about 278.6768053043.

Adding to 21642253 its reverse (35224612), we get a palindrome (56866865).

The spelling of 21642253 in words is "twenty-one million, six hundred forty-two thousand, two hundred fifty-three".