21539653 has 2 divisors, whose sum is σ = 21539654. Its totient is φ = 21539652.

The previous prime is 21539621. The next prime is 21539657. The reversal of 21539653 is 35693512.

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., 18378369 + 3161284 = 4287^2 + 1778^2 .

It is a cyclic number.

It is not a de Polignac number, because 21539653 - 2⁵ = 21539621 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21539657) 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, 10769826 + 10769827.

It is an arithmetic number, because the mean of its divisors is an integer number (10769827).

Almost surely, 2^21539653 is an apocalyptic number.

It is an amenable number.

21539653 is a deficient number, since it is larger than the sum of its proper divisors (1).

21539653 is an equidigital number, since it uses as much as digits as its factorization.

21539653 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24300, while the sum is 34.

The square root of 21539653 is about 4641.0831709850. The cubic root of 21539653 is about 278.2357307350.

The spelling of 21539653 in words is "twenty-one million, five hundred thirty-nine thousand, six hundred fifty-three".