21103561 has 8 divisors (see below), whose sum is σ = 22365000. Its totient is φ = 19877760.

The previous prime is 21103559. The next prime is 21103603. The reversal of 21103561 is 16530112.

It can be written as a sum of positive squares in 4 ways, for example, as 455625 + 20647936 = 675^2 + 4544^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21103561 - 2¹ = 21103559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21103501) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 7686 + ... + 10063.

It is an arithmetic number, because the mean of its divisors is an integer number (2795625).

Almost surely, 2^21103561 is an apocalyptic number.

It is an amenable number.

21103561 is a deficient number, since it is larger than the sum of its proper divisors (1261439).

21103561 is a wasteful number, since it uses less digits than its factorization.

21103561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17819.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 21103561 is about 4593.8612299459. The cubic root of 21103561 is about 276.3451931308.

Adding to 21103561 its reverse (16530112), we get a palindrome (37633673).

It can be divided in two parts, 2110 and 3561, that added together give a triangular number (5671 = T₁₀₆).

The spelling of 21103561 in words is "twenty-one million, one hundred three thousand, five hundred sixty-one".