21561413 has 8 divisors (see below), whose sum is σ = 22357080. Its totient is φ = 20769280.

The previous prime is 21561401. The next prime is 21561427. The reversal of 21561413 is 31416512.

It can be written as a sum of positive squares in 4 ways, for example, as 1909924 + 19651489 = 1382^2 + 4433^2 .

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 21561413 - 2⁶ = 21561349 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21561443) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21581 + ... + 22557.

It is an arithmetic number, because the mean of its divisors is an integer number (2794635).

Almost surely, 2^21561413 is an apocalyptic number.

It is an amenable number.

21561413 is a deficient number, since it is larger than the sum of its proper divisors (795667).

21561413 is an equidigital number, since it uses as much as digits as its factorization.

21561413 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1767.

The product of its digits is 720, while the sum is 23.

The square root of 21561413 is about 4643.4268595510. The cubic root of 21561413 is about 278.3293932136.

Adding to 21561413 its reverse (31416512), we get a palindrome (52977925).

The spelling of 21561413 in words is "twenty-one million, five hundred sixty-one thousand, four hundred thirteen".