21561365 has 16 divisors (see below), whose sum is σ = 30057600. Its totient is φ = 14541120.

The previous prime is 21561359. The next prime is 21561377. The reversal of 21561365 is 56316512.

It is not a de Polignac number, because 21561365 - 2⁴ = 21561349 is a prime.

It is a congruent number.

It is an unprimeable number.

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 15 ways as a sum of consecutive naturals, for example, 2915 + ... + 7184.

It is an arithmetic number, because the mean of its divisors is an integer number (1878600).

Almost surely, 2^21561365 is an apocalyptic number.

It is an amenable number.

21561365 is a deficient number, since it is larger than the sum of its proper divisors (8496235).

21561365 is a wasteful number, since it uses less digits than its factorization.

21561365 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10172.

The product of its digits is 5400, while the sum is 29.

The square root of 21561365 is about 4643.4216909516. The cubic root of 21561365 is about 278.3291866745.

Adding to 21561365 its reverse (56316512), we get a palindrome (77877877).

The spelling of 21561365 in words is "twenty-one million, five hundred sixty-one thousand, three hundred sixty-five".