21663553 has 8 divisors (see below), whose sum is σ = 23117600. Its totient is φ = 20240928.

The previous prime is 21663547. The next prime is 21663589. The reversal of 21663553 is 35536612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21663553 - 2⁹ = 21663041 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21663053) 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 7 ways as a sum of consecutive naturals, for example, 6423 + ... + 9196.

It is an arithmetic number, because the mean of its divisors is an integer number (2889700).

Almost surely, 2^21663553 is an apocalyptic number.

It is an amenable number.

21663553 is a deficient number, since it is larger than the sum of its proper divisors (1454047).

21663553 is a wasteful number, since it uses less digits than its factorization.

21663553 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15711.

The product of its digits is 16200, while the sum is 31.

The square root of 21663553 is about 4654.4122077874. The cubic root of 21663553 is about 278.7681985880.

The spelling of 21663553 in words is "twenty-one million, six hundred sixty-three thousand, five hundred fifty-three".