21781436905 has 8 divisors (see below), whose sum is σ = 26251864200. Its totient is φ = 17349056256.

The previous prime is 21781436903. The next prime is 21781436909. The reversal of 21781436905 is 50963418712.

It can be written as a sum of positive squares in 4 ways, for example, as 12835303849 + 8946133056 = 113293^2 + 94584^2 .

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 21781436905 - 2¹ = 21781436903 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21781436903) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9510400 + ... + 9512689.

It is an arithmetic number, because the mean of its divisors is an integer number (3281483025).

It is a 1-persistent number, because it is pandigital, but 2⋅21781436905 = 43562873810 is not.

Almost surely, 2^21781436905 is an apocalyptic number.

It is an amenable number.

21781436905 is a deficient number, since it is larger than the sum of its proper divisors (4470427295).

21781436905 is a wasteful number, since it uses less digits than its factorization.

21781436905 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 19023323.

The product of its (nonzero) digits is 362880, while the sum is 46.

The spelling of 21781436905 in words is "twenty-one billion, seven hundred eighty-one million, four hundred thirty-six thousand, nine hundred five".