21261204 has 60 divisors (see below), whose sum is σ = 56023968. Its totient is φ = 7030800.

The previous prime is 21261193. The next prime is 21261211. The reversal of 21261204 is 40216212.

Added to its reverse (40216212) it gives a triangular number (61477416 = T₁₁₀₈₈).

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a zygodrome in base 3.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 68209 + ... + 68519.

Almost surely, 2^21261204 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21261204, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28011984).

21261204 is an abundant number, since it is smaller than the sum of its proper divisors (34762764).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21261204 is a wasteful number, since it uses less digits than its factorization.

21261204 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 538 (or 527 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21261204 is about 4610.9873129298. The cubic root of 21261204 is about 277.0315837602.

Adding to 21261204 its reverse (40216212), we get a palindrome (61477416).

It can be divided in two parts, 212 and 61204, that added together give a palindrome (61416).

The spelling of 21261204 in words is "twenty-one million, two hundred sixty-one thousand, two hundred four".