21559961 has 4 divisors (see below), whose sum is σ = 22828212. Its totient is φ = 20291712.

The previous prime is 21559949. The next prime is 21559991. The reversal of 21559961 is 16995512.

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 12673600 + 8886361 = 3560^2 + 2981^2 .

It is a cyclic number.

It is not a de Polignac number, because 21559961 - 2⁶ = 21559897 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21559991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 634100 + ... + 634133.

It is an arithmetic number, because the mean of its divisors is an integer number (5707053).

Almost surely, 2^21559961 is an apocalyptic number.

It is an amenable number.

21559961 is a deficient number, since it is larger than the sum of its proper divisors (1268251).

21559961 is a wasteful number, since it uses less digits than its factorization.

21559961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1268250.

The product of its digits is 24300, while the sum is 38.

The square root of 21559961 is about 4643.2705068734. The cubic root of 21559961 is about 278.3231452719.

The spelling of 21559961 in words is "twenty-one million, five hundred fifty-nine thousand, nine hundred sixty-one".