21108761 has 4 divisors (see below), whose sum is σ = 21119412. Its totient is φ = 21098112.

The previous prime is 21108757. The next prime is 21108793. The reversal of 21108761 is 16780112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 7529536 + 13579225 = 2744^2 + 3685^2 .

It is a cyclic number.

It is not a de Polignac number, because 21108761 - 2² = 21108757 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 21108761.

It is not an unprimeable number, because it can be changed into a prime (21108701) 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, 1376 + ... + 6641.

It is an arithmetic number, because the mean of its divisors is an integer number (5279853).

Almost surely, 2^21108761 is an apocalyptic number.

It is an amenable number.

21108761 is a deficient number, since it is larger than the sum of its proper divisors (10651).

21108761 is an equidigital number, since it uses as much as digits as its factorization.

21108761 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10650.

The product of its (nonzero) digits is 672, while the sum is 26.

The square root of 21108761 is about 4594.4271677762. The cubic root of 21108761 is about 276.3678887791.

Adding to 21108761 its reverse (16780112), we get a palindrome (37888873).

The spelling of 21108761 in words is "twenty-one million, one hundred eight thousand, seven hundred sixty-one".