21553651 has 4 divisors (see below), whose sum is σ = 24632752. Its totient is φ = 18474552.

The previous prime is 21553643. The next prime is 21553717. The reversal of 21553651 is 15635512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21553651 - 2³ = 21553643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21553951) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1539540 + ... + 1539553.

It is an arithmetic number, because the mean of its divisors is an integer number (6158188).

Almost surely, 2^21553651 is an apocalyptic number.

21553651 is a deficient number, since it is larger than the sum of its proper divisors (3079101).

21553651 is an equidigital number, since it uses as much as digits as its factorization.

21553651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3079100.

The product of its digits is 4500, while the sum is 28.

The square root of 21553651 is about 4642.5909791839. The cubic root of 21553651 is about 278.2959901454.

The spelling of 21553651 in words is "twenty-one million, five hundred fifty-three thousand, six hundred fifty-one".