21510040561 has 4 divisors (see below), whose sum is σ = 21751726500. Its totient is φ = 21268354624.

The previous prime is 21510040529. The next prime is 21510040579. The reversal of 21510040561 is 16504001512.

It is a happy number.

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 2488114161 + 19021926400 = 49881^2 + 137920^2 .

It is a cyclic number.

It is not a de Polignac number, because 21510040561 - 2⁵ = 21510040529 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21510040261) 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, 120842836 + ... + 120843013.

It is an arithmetic number, because the mean of its divisors is an integer number (5437931625).

Almost surely, 2^21510040561 is an apocalyptic number.

It is an amenable number.

21510040561 is a deficient number, since it is larger than the sum of its proper divisors (241685939).

21510040561 is an equidigital number, since it uses as much as digits as its factorization.

21510040561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 241685938.

The product of its (nonzero) digits is 1200, while the sum is 25.

The spelling of 21510040561 in words is "twenty-one billion, five hundred ten million, forty thousand, five hundred sixty-one".