21557171 has 6 divisors (see below), whose sum is σ = 21725172. Its totient is φ = 21390440.

The previous prime is 21557143. The next prime is 21557177. The reversal of 21557171 is 17175512.

It is not a de Polignac number, because 21557171 - 2¹⁴ = 21540787 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21557177) 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, 21716 + ... + 22686.

It is an arithmetic number, because the mean of its divisors is an integer number (3620862).

Almost surely, 2^21557171 is an apocalyptic number.

21557171 is a deficient number, since it is larger than the sum of its proper divisors (168001).

21557171 is an frugal number, since it uses more digits than its factorization.

21557171 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1269 (or 1120 counting only the distinct ones).

The product of its digits is 2450, while the sum is 29.

The square root of 21557171 is about 4642.9700623631. The cubic root of 21557171 is about 278.3111391421.

The spelling of 21557171 in words is "twenty-one million, five hundred fifty-seven thousand, one hundred seventy-one".