21231555 has 32 divisors (see below), whose sum is σ = 36288000. Its totient is φ = 10563072.

The previous prime is 21231547. The next prime is 21231557. The reversal of 21231555 is 55513212.

It is a happy number.

It is not a de Polignac number, because 21231555 - 2³ = 21231547 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21231557) 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, 35146 + ... + 35744.

It is an arithmetic number, because the mean of its divisors is an integer number (1134000).

Almost surely, 2^21231555 is an apocalyptic number.

21231555 is a deficient number, since it is larger than the sum of its proper divisors (15056445).

21231555 is a wasteful number, since it uses less digits than its factorization.

21231555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 763.

The product of its digits is 1500, while the sum is 24.

The square root of 21231555 is about 4607.7711531716. The cubic root of 21231555 is about 276.9027492498.

Adding to 21231555 its reverse (55513212), we get a palindrome (76744767).

The spelling of 21231555 in words is "twenty-one million, two hundred thirty-one thousand, five hundred fifty-five".