21335561 has 16 divisors (see below), whose sum is σ = 25174800. Its totient is φ = 17891328.

The previous prime is 21335557. The next prime is 21335563. The reversal of 21335561 is 16553312.

It can be written as a sum of positive squares in 8 ways, for example, as 175561 + 21160000 = 419^2 + 4600^2 .

It is not a de Polignac number, because 21335561 - 2² = 21335557 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21335561.

It is not an unprimeable number, because it can be changed into a prime (21335563) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4745 + ... + 8073.

It is an arithmetic number, because the mean of its divisors is an integer number (1573425).

Almost surely, 2^21335561 is an apocalyptic number.

It is an amenable number.

21335561 is a deficient number, since it is larger than the sum of its proper divisors (3839239).

21335561 is a wasteful number, since it uses less digits than its factorization.

21335561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3388.

The product of its digits is 2700, while the sum is 26.

The square root of 21335561 is about 4619.0432992125. The cubic root of 21335561 is about 277.3541630155.

Adding to 21335561 its reverse (16553312), we get a palindrome (37888873).

The spelling of 21335561 in words is "twenty-one million, three hundred thirty-five thousand, five hundred sixty-one".