21263561 has 8 divisors (see below), whose sum is σ = 23491200. Its totient is φ = 19085040.

The previous prime is 21263537. The next prime is 21263579. The reversal of 21263561 is 16536212.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21263561 - 2⁶ = 21263497 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21263561.

It is not an unprimeable number, because it can be changed into a prime (21263161) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11366 + ... + 13103.

It is an arithmetic number, because the mean of its divisors is an integer number (2936400).

Almost surely, 2^21263561 is an apocalyptic number.

It is an amenable number.

21263561 is a deficient number, since it is larger than the sum of its proper divisors (2227639).

21263561 is a wasteful number, since it uses less digits than its factorization.

21263561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 24559.

The product of its digits is 2160, while the sum is 26.

The square root of 21263561 is about 4611.2428910219. The cubic root of 21263561 is about 277.0418205483.

Adding to 21263561 its reverse (16536212), we get a palindrome (37799773).

The spelling of 21263561 in words is "twenty-one million, two hundred sixty-three thousand, five hundred sixty-one".