21157553 has 6 divisors (see below), whose sum is σ = 21322854. Its totient is φ = 20993504.

The previous prime is 21157529. The next prime is 21157573. The reversal of 21157553 is 35575112.

It is a happy number.

It can be written as a sum of positive squares in 3 ways, for example, as 153664 + 21003889 = 392^2 + 4583^2 .

It is not a de Polignac number, because 21157553 - 2¹⁰ = 21156529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21157523) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 21725 + ... + 22677.

It is an arithmetic number, because the mean of its divisors is an integer number (3553809).

Almost surely, 2^21157553 is an apocalyptic number.

It is an amenable number.

21157553 is a deficient number, since it is larger than the sum of its proper divisors (165301).

21157553 is an frugal number, since it uses more digits than its factorization.

21157553 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1251 (or 1102 counting only the distinct ones).

The product of its digits is 5250, while the sum is 29.

The square root of 21157553 is about 4599.7340140491. The cubic root of 21157553 is about 276.5806624501.

The spelling of 21157553 in words is "twenty-one million, one hundred fifty-seven thousand, five hundred fifty-three".