21555555 has 32 divisors (see below), whose sum is σ = 40780800. Its totient is φ = 9512832.

The previous prime is 21555553. The next prime is 21555559. The reversal of 21555555 is 55555512.

It is not a de Polignac number, because 21555555 - 2¹ = 21555553 is a prime.

21555555 is a modest number, since divided by 5555 gives 2155 as remainder.

It is not an unprimeable number, because it can be changed into a prime (21555553) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 495 + ... + 6584.

It is an arithmetic number, because the mean of its divisors is an integer number (1274400).

Almost surely, 2^21555555 is an apocalyptic number.

21555555 is a deficient number, since it is larger than the sum of its proper divisors (19225245).

21555555 is a wasteful number, since it uses less digits than its factorization.

21555555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7123.

The product of its digits is 31250, while the sum is 33.

The square root of 21555555 is about 4642.7960325649. The cubic root of 21555555 is about 278.3041845802.

The spelling of 21555555 in words is "twenty-one million, five hundred fifty-five thousand, five hundred fifty-five".