21085555 has 4 divisors (see below), whose sum is σ = 25302672. Its totient is φ = 16868440.

The previous prime is 21085543. The next prime is 21085567. The reversal of 21085555 is 55558012.

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

It is an interprime number because it is at equal distance from previous prime (21085543) and next prime (21085567).

It is not a de Polignac number, because 21085555 - 2²³ = 12696947 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, 2108551 + ... + 2108560.

It is an arithmetic number, because the mean of its divisors is an integer number (6325668).

Almost surely, 2^21085555 is an apocalyptic number.

21085555 is a deficient number, since it is larger than the sum of its proper divisors (4217117).

21085555 is an equidigital number, since it uses as much as digits as its factorization.

21085555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4217116.

The product of its (nonzero) digits is 10000, while the sum is 31.

The square root of 21085555 is about 4591.9010224525. The cubic root of 21085555 is about 276.2665762662.

The spelling of 21085555 in words is "twenty-one million, eighty-five thousand, five hundred fifty-five".