21681329861 has 4 divisors (see below), whose sum is σ = 21683570400. Its totient is φ = 21679089324.

The previous prime is 21681329851. The next prime is 21681329863. The reversal of 21681329861 is 16892318612.

It is a happy number.

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 a de Polignac number, because none of the positive numbers 2^k-21681329861 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681329863) 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, 1105691 + ... + 1125128.

It is an arithmetic number, because the mean of its divisors is an integer number (5420892600).

Almost surely, 2^21681329861 is an apocalyptic number.

It is an amenable number.

21681329861 is a deficient number, since it is larger than the sum of its proper divisors (2240539).

21681329861 is an equidigital number, since it uses as much as digits as its factorization.

21681329861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2240538.

The product of its digits is 248832, while the sum is 47.

The spelling of 21681329861 in words is "twenty-one billion, six hundred eighty-one million, three hundred twenty-nine thousand, eight hundred sixty-one".