21221305405 has 8 divisors (see below), whose sum is σ = 25466381784. Its totient is φ = 16976500800.

The previous prime is 21221305381. The next prime is 21221305421. The reversal of 21221305405 is 50450312212.

It can be written as a sum of positive squares in 4 ways, for example, as 6057353241 + 15163952164 = 77829^2 + 123142^2 .

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

It is not a de Polignac number, because 21221305405 - 2¹³ = 21221297213 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21221305405.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 199695 + ... + 286915.

It is an arithmetic number, because the mean of its divisors is an integer number (3183297723).

Almost surely, 2^21221305405 is an apocalyptic number.

It is an amenable number.

21221305405 is a deficient number, since it is larger than the sum of its proper divisors (4245076379).

21221305405 is an equidigital number, since it uses as much as digits as its factorization.

21221305405 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 135887.

The product of its (nonzero) digits is 2400, while the sum is 25.

Adding to 21221305405 its reverse (50450312212), we get a palindrome (71671617617).

The spelling of 21221305405 in words is "twenty-one billion, two hundred twenty-one million, three hundred five thousand, four hundred five".