21671553 has 4 divisors (see below), whose sum is σ = 28895408. Its totient is φ = 14447700.

The previous prime is 21671539. The next prime is 21671557. The reversal of 21671553 is 35517612.

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 not a de Polignac number, because 21671553 - 2⁵ = 21671521 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21671553.

It is not an unprimeable number, because it can be changed into a prime (21671557) 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, 3611923 + ... + 3611928.

It is an arithmetic number, because the mean of its divisors is an integer number (7223852).

Almost surely, 2^21671553 is an apocalyptic number.

It is an amenable number.

21671553 is a deficient number, since it is larger than the sum of its proper divisors (7223855).

21671553 is an equidigital number, since it uses as much as digits as its factorization.

21671553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7223854.

The product of its digits is 6300, while the sum is 30.

The square root of 21671553 is about 4655.2715280636. The cubic root of 21671553 is about 278.8025092283.

The spelling of 21671553 in words is "twenty-one million, six hundred seventy-one thousand, five hundred fifty-three".