21555320351 has 4 divisors (see below), whose sum is σ = 21555651600. Its totient is φ = 21554989104.

The previous prime is 21555320341. The next prime is 21555320363. The reversal of 21555320351 is 15302355512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21555320351 - 2²⁶ = 21488211487 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 (21555320341) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 32171 + ... + 210108.

It is an arithmetic number, because the mean of its divisors is an integer number (5388912900).

Almost surely, 2^21555320351 is an apocalyptic number.

21555320351 is a deficient number, since it is larger than the sum of its proper divisors (331249).

21555320351 is an equidigital number, since it uses as much as digits as its factorization.

21555320351 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331248.

The product of its (nonzero) digits is 22500, while the sum is 32.

Adding to 21555320351 its reverse (15302355512), we get a palindrome (36857675863).

The spelling of 21555320351 in words is "twenty-one billion, five hundred fifty-five million, three hundred twenty thousand, three hundred fifty-one".