21215555 has 16 divisors (see below), whose sum is σ = 26335584. Its totient is φ = 16396800.

The previous prime is 21215543. The next prime is 21215561. The reversal of 21215555 is 55551212.

It is not a de Polignac number, because 21215555 - 2⁴ = 21215539 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 21227 + ... + 22203.

It is an arithmetic number, because the mean of its divisors is an integer number (1645974).

Almost surely, 2^21215555 is an apocalyptic number.

21215555 is a deficient number, since it is larger than the sum of its proper divisors (5120029).

21215555 is a wasteful number, since it uses less digits than its factorization.

21215555 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1126.

The product of its digits is 2500, while the sum is 26.

The square root of 21215555 is about 4606.0346286149. The cubic root of 21215555 is about 276.8331742332.

Adding to 21215555 its reverse (55551212), we get a palindrome (76766767).

The spelling of 21215555 in words is "twenty-one million, two hundred fifteen thousand, five hundred fifty-five".