21260561 has 6 divisors (see below), whose sum is σ = 24731730. Its totient is φ = 18223296.

The previous prime is 21260549. The next prime is 21260609. The reversal of 21260561 is 16506212.

It can be written as a sum of positive squares in only one way, i.e., 19140625 + 2119936 = 4375^2 + 1456^2 .

It is not a de Polignac number, because 21260561 - 2¹⁴ = 21244177 is a prime.

It is a super-2 number, since 2×21260561² = 904022908069442, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21260501) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 216896 + ... + 216993.

It is an arithmetic number, because the mean of its divisors is an integer number (4121955).

Almost surely, 2^21260561 is an apocalyptic number.

It is an amenable number.

21260561 is a deficient number, since it is larger than the sum of its proper divisors (3471169).

21260561 is an equidigital number, since it uses as much as digits as its factorization.

21260561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 433903 (or 433896 counting only the distinct ones).

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21260561 is about 4610.9175876391. The cubic root of 21260561 is about 277.0287909879.

Adding to 21260561 its reverse (16506212), we get a palindrome (37766773).

The spelling of 21260561 in words is "twenty-one million, two hundred sixty thousand, five hundred sixty-one".