21518009681 has 8 divisors (see below), whose sum is σ = 24609183744. Its totient is φ = 18431128800.

The previous prime is 21518009659. The next prime is 21518009687. The reversal of 21518009681 is 18690081512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21518009681 - 2¹⁰ = 21518008657 is a prime.

It is a super-2 number, since 2×21518009681² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21518009687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1062545 + ... + 1082606.

It is an arithmetic number, because the mean of its divisors is an integer number (3076147968).

Almost surely, 2^21518009681 is an apocalyptic number.

It is an amenable number.

21518009681 is a deficient number, since it is larger than the sum of its proper divisors (3091174063).

21518009681 is a wasteful number, since it uses less digits than its factorization.

21518009681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2146591.

The product of its (nonzero) digits is 34560, while the sum is 41.

The spelling of 21518009681 in words is "twenty-one billion, five hundred eighteen million, nine thousand, six hundred eighty-one".