21255421555 has 8 divisors (see below), whose sum is σ = 27006888672. Its totient is φ = 16004082048.

The previous prime is 21255421541. The next prime is 21255421571. The reversal of 21255421555 is 55512455212.

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 21255421555 - 2¹⁹ = 21254897267 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 125031807 + ... + 125031976.

It is an arithmetic number, because the mean of its divisors is an integer number (3375861084).

Almost surely, 2^21255421555 is an apocalyptic number.

21255421555 is a deficient number, since it is larger than the sum of its proper divisors (5751467117).

21255421555 is a wasteful number, since it uses less digits than its factorization.

21255421555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 250063805.

The product of its digits is 100000, while the sum is 37.

Adding to 21255421555 its reverse (55512455212), we get a palindrome (76767876767).

The spelling of 21255421555 in words is "twenty-one billion, two hundred fifty-five million, four hundred twenty-one thousand, five hundred fifty-five".