21211561 has 12 divisors (see below), whose sum is σ = 24796368. Its totient is φ = 18091752.

The previous prime is 21211507. The next prime is 21211577. The reversal of 21211561 is 16511212.

It is not a de Polignac number, because 21211561 - 2⁷ = 21211433 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21215561) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10170 + ... + 12076.

It is an arithmetic number, because the mean of its divisors is an integer number (2066364).

Almost surely, 2^21211561 is an apocalyptic number.

It is an amenable number.

21211561 is a deficient number, since it is larger than the sum of its proper divisors (3584807).

21211561 is a wasteful number, since it uses less digits than its factorization.

21211561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2148 (or 2141 counting only the distinct ones).

The product of its digits is 120, while the sum is 19.

The square root of 21211561 is about 4605.6010465519. The cubic root of 21211561 is about 276.8158011141.

Adding to 21211561 its reverse (16511212), we get a palindrome (37722773).

The spelling of 21211561 in words is "twenty-one million, two hundred eleven thousand, five hundred sixty-one".