21240985681 has 4 divisors (see below), whose sum is σ = 21253729392. Its totient is φ = 21228241972.

The previous prime is 21240985657. The next prime is 21240985687. The reversal of 21240985681 is 18658904212.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21240985681 - 2¹⁵ = 21240952913 is a prime.

It is a super-2 number, since 2×21240985681² (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 (21240985687) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6369355 + ... + 6372688.

It is an arithmetic number, because the mean of its divisors is an integer number (5313432348).

Almost surely, 2^21240985681 is an apocalyptic number.

It is an amenable number.

21240985681 is a deficient number, since it is larger than the sum of its proper divisors (12743711).

21240985681 is a wasteful number, since it uses less digits than its factorization.

21240985681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 12743710.

The product of its (nonzero) digits is 276480, while the sum is 46.

The spelling of 21240985681 in words is "twenty-one billion, two hundred forty million, nine hundred eighty-five thousand, six hundred eighty-one".