21051617 has 4 divisors (see below), whose sum is σ = 21158676. Its totient is φ = 20944560.

The previous prime is 21051599. The next prime is 21051623. The reversal of 21051617 is 71615012.

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

It can be written as a sum of positive squares in 2 ways, for example, as 17380561 + 3671056 = 4169^2 + 1916^2 .

It is a cyclic number.

It is not a de Polignac number, because 21051617 - 2¹⁴ = 21035233 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21051592 and 21051601.

It is not an unprimeable number, because it can be changed into a prime (21051637) 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, 53234 + ... + 53627.

It is an arithmetic number, because the mean of its divisors is an integer number (5289669).

Almost surely, 2^21051617 is an apocalyptic number.

It is an amenable number.

21051617 is a deficient number, since it is larger than the sum of its proper divisors (107059).

21051617 is a wasteful number, since it uses less digits than its factorization.

21051617 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 107058.

The product of its (nonzero) digits is 420, while the sum is 23.

The square root of 21051617 is about 4588.2041149016. The cubic root of 21051617 is about 276.1182761642.

Adding to 21051617 its reverse (71615012), we get a palindrome (92666629).

The spelling of 21051617 in words is "twenty-one million, fifty-one thousand, six hundred seventeen".