21231556 has 12 divisors (see below), whose sum is σ = 37679040. Its totient is φ = 10466120.

The previous prime is 21231547. The next prime is 21231557. The reversal of 21231556 is 65513212.

It is a super-2 number, since 2×21231556² = 901557940362272, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21231556.

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 3 ways as a sum of consecutive naturals, for example, 37096 + ... + 37663.

It is an arithmetic number, because the mean of its divisors is an integer number (3139920).

Almost surely, 2^21231556 is an apocalyptic number.

It is an amenable number.

21231556 is a deficient number, since it is larger than the sum of its proper divisors (16447484).

21231556 is a wasteful number, since it uses less digits than its factorization.

21231556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 74834 (or 74832 counting only the distinct ones).

The product of its digits is 1800, while the sum is 25.

The square root of 21231556 is about 4607.7712616839. The cubic root of 21231556 is about 276.9027535971.

Adding to 21231556 its reverse (65513212), we get a palindrome (86744768).

The spelling of 21231556 in words is "twenty-one million, two hundred thirty-one thousand, five hundred fifty-six".