21808453 has 2 divisors, whose sum is σ = 21808454. Its totient is φ = 21808452.

The previous prime is 21808441. The next prime is 21808483. The reversal of 21808453 is 35480812.

It is the 1907-th star number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 14615329 + 7193124 = 3823^2 + 2682^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21808453 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21808483) 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, 10904226 + 10904227.

It is an arithmetic number, because the mean of its divisors is an integer number (10904227).

Almost surely, 2^21808453 is an apocalyptic number.

It is an amenable number.

21808453 is a deficient number, since it is larger than the sum of its proper divisors (1).

21808453 is an equidigital number, since it uses as much as digits as its factorization.

21808453 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 7680, while the sum is 31.

The square root of 21808453 is about 4669.9521410824. The cubic root of 21808453 is about 279.3883459501.

The spelling of 21808453 in words is "twenty-one million, eight hundred eight thousand, four hundred fifty-three".