21505008611 has 4 divisors (see below), whose sum is σ = 21505366752. Its totient is φ = 21504650472.

The previous prime is 21505008599. The next prime is 21505008647. The reversal of 21505008611 is 11680050512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21505008611 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21505008011) 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, 64616 + ... + 217221.

It is an arithmetic number, because the mean of its divisors is an integer number (5376341688).

Almost surely, 2^21505008611 is an apocalyptic number.

21505008611 is a deficient number, since it is larger than the sum of its proper divisors (358141).

21505008611 is an equidigital number, since it uses as much as digits as its factorization.

21505008611 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 358140.

The product of its (nonzero) digits is 2400, while the sum is 29.

The spelling of 21505008611 in words is "twenty-one billion, five hundred five million, eight thousand, six hundred eleven".