21140561 has 4 divisors (see below), whose sum is σ = 22766772. Its totient is φ = 19514352.

The previous prime is 21140549. The next prime is 21140569. The reversal of 21140561 is 16504112.

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 4330561 + 16810000 = 2081^2 + 4100^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21140561 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21140569) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 813086 + ... + 813111.

It is an arithmetic number, because the mean of its divisors is an integer number (5691693).

Almost surely, 2^21140561 is an apocalyptic number.

It is an amenable number.

21140561 is a deficient number, since it is larger than the sum of its proper divisors (1626211).

21140561 is a wasteful number, since it uses less digits than its factorization.

21140561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1626210.

The product of its (nonzero) digits is 240, while the sum is 20.

The square root of 21140561 is about 4597.8865797233. The cubic root of 21140561 is about 276.5066003676.

Adding to 21140561 its reverse (16504112), we get a palindrome (37644673).

The spelling of 21140561 in words is "twenty-one million, one hundred forty thousand, five hundred sixty-one".