21505766518 has 4 divisors (see below), whose sum is σ = 32258649780. Its totient is φ = 10752883258.

The previous prime is 21505766467. The next prime is 21505766519. The reversal of 21505766518 is 81566750512.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21505766519) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5376441628 + ... + 5376441631.

It is an arithmetic number, because the mean of its divisors is an integer number (8064662445).

Almost surely, 2^21505766518 is an apocalyptic number.

21505766518 is a deficient number, since it is larger than the sum of its proper divisors (10752883262).

21505766518 is a wasteful number, since it uses less digits than its factorization.

21505766518 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10752883261.

The product of its (nonzero) digits is 504000, while the sum is 46.

The spelling of 21505766518 in words is "twenty-one billion, five hundred five million, seven hundred sixty-six thousand, five hundred eighteen".