21983561 has 4 divisors (see below), whose sum is σ = 22939392. Its totient is φ = 21027732.

The previous prime is 21983531. The next prime is 21983569. The reversal of 21983561 is 16538912.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21983561 - 2¹⁰ = 21982537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21983569) 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, 477881 + ... + 477926.

It is an arithmetic number, because the mean of its divisors is an integer number (5734848).

Almost surely, 2^21983561 is an apocalyptic number.

It is an amenable number.

21983561 is a deficient number, since it is larger than the sum of its proper divisors (955831).

21983561 is an equidigital number, since it uses as much as digits as its factorization.

21983561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 955830.

The product of its digits is 12960, while the sum is 35.

The square root of 21983561 is about 4688.6630290521. The cubic root of 21983561 is about 280.1341236679.

The spelling of 21983561 in words is "twenty-one million, nine hundred eighty-three thousand, five hundred sixty-one".