21781250405 has 8 divisors (see below), whose sum is σ = 26143671672. Its totient is φ = 17420886208.

The previous prime is 21781250399. The next prime is 21781250437. The reversal of 21781250405 is 50405218712.

It can be written as a sum of positive squares in 4 ways, for example, as 254785444 + 21526464961 = 15962^2 + 146719^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21781250405 - 2³² = 17486283109 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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, 490874 + ... + 533403.

It is an arithmetic number, because the mean of its divisors is an integer number (3267958959).

Almost surely, 2^21781250405 is an apocalyptic number.

It is an amenable number.

21781250405 is a deficient number, since it is larger than the sum of its proper divisors (4362421267).

21781250405 is a wasteful number, since it uses less digits than its factorization.

21781250405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1028535.

The product of its (nonzero) digits is 22400, while the sum is 35.

The spelling of 21781250405 in words is "twenty-one billion, seven hundred eighty-one million, two hundred fifty thousand, four hundred five".