21517171 has 4 divisors (see below), whose sum is σ = 23172352. Its totient is φ = 19861992.

The previous prime is 21517163. The next prime is 21517187. The reversal of 21517171 is 17171512.

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 21517171 - 2³ = 21517163 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21517271) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 827571 + ... + 827596.

It is an arithmetic number, because the mean of its divisors is an integer number (5793088).

Almost surely, 2^21517171 is an apocalyptic number.

21517171 is a deficient number, since it is larger than the sum of its proper divisors (1655181).

21517171 is a wasteful number, since it uses less digits than its factorization.

21517171 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1655180.

The product of its digits is 490, while the sum is 25.

The square root of 21517171 is about 4638.6604747491. The cubic root of 21517171 is about 278.1388942434.

Adding to 21517171 its reverse (17171512), we get a palindrome (38688683).

The spelling of 21517171 in words is "twenty-one million, five hundred seventeen thousand, one hundred seventy-one".