21561481 has 2 divisors, whose sum is σ = 21561482. Its totient is φ = 21561480.

The previous prime is 21561479. The next prime is 21561497. The reversal of 21561481 is 18416512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20169081 + 1392400 = 4491^2 + 1180^2 .

It is a cyclic number.

It is not a de Polignac number, because 21561481 - 2¹ = 21561479 is a prime.

It is a super-2 number, since 2×21561481² = 929794925826722, which contains 22 as substring.

Together with 21561479, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21561401) 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 as a sum of consecutive naturals, namely, 10780740 + 10780741.

It is an arithmetic number, because the mean of its divisors is an integer number (10780741).

Almost surely, 2^21561481 is an apocalyptic number.

It is an amenable number.

21561481 is a deficient number, since it is larger than the sum of its proper divisors (1).

21561481 is an equidigital number, since it uses as much as digits as its factorization.

21561481 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1920, while the sum is 28.

The square root of 21561481 is about 4643.4341817237. The cubic root of 21561481 is about 278.3296858100.

Adding to 21561481 its reverse (18416512), we get a palindrome (39977993).

The spelling of 21561481 in words is "twenty-one million, five hundred sixty-one thousand, four hundred eighty-one".