21005617 has 4 divisors (see below), whose sum is σ = 21018736. Its totient is φ = 20992500.

The previous prime is 21005609. The next prime is 21005623. The reversal of 21005617 is 71650012.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21005617 - 2³ = 21005609 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21005627) 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, 3759 + ... + 7492.

It is an arithmetic number, because the mean of its divisors is an integer number (5254684).

Almost surely, 2^21005617 is an apocalyptic number.

It is an amenable number.

21005617 is a deficient number, since it is larger than the sum of its proper divisors (13119).

21005617 is a wasteful number, since it uses less digits than its factorization.

21005617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13118.

The product of its (nonzero) digits is 420, while the sum is 22.

The square root of 21005617 is about 4583.1885189244. The cubic root of 21005617 is about 275.9170136629.

Adding to 21005617 its reverse (71650012), we get a palindrome (92655629).

The spelling of 21005617 in words is "twenty-one million, five thousand, six hundred seventeen".