21019555 has 4 divisors (see below), whose sum is σ = 25223472. Its totient is φ = 16815640.

The previous prime is 21019549. The next prime is 21019571. The reversal of 21019555 is 55591012.

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

It is not a de Polignac number, because 21019555 - 2⁹ = 21019043 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2101951 + ... + 2101960.

It is an arithmetic number, because the mean of its divisors is an integer number (6305868).

Almost surely, 2^21019555 is an apocalyptic number.

21019555 is a deficient number, since it is larger than the sum of its proper divisors (4203917).

21019555 is an equidigital number, since it uses as much as digits as its factorization.

21019555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4203916.

The product of its (nonzero) digits is 2250, while the sum is 28.

The square root of 21019555 is about 4584.7088239058. The cubic root of 21019555 is about 275.9780272013.

The spelling of 21019555 in words is "twenty-one million, nineteen thousand, five hundred fifty-five".