21206406 has 32 divisors (see below), whose sum is σ = 46434528. Its totient is φ = 6416640.

The previous prime is 21206401. The next prime is 21206407. The reversal of 21206406 is 60460212.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21206401) by changing a digit.

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 15 ways as a sum of consecutive naturals, for example, 2530 + ... + 6986.

It is an arithmetic number, because the mean of its divisors is an integer number (1451079).

Almost surely, 2^21206406 is an apocalyptic number.

21206406 is a gapful number since it is divisible by the number (26) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 21206406, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23217264).

21206406 is an abundant number, since it is smaller than the sum of its proper divisors (25228122).

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

21206406 is a wasteful number, since it uses less digits than its factorization.

21206406 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4536.

The product of its (nonzero) digits is 576, while the sum is 21.

The square root of 21206406 is about 4605.0413678924. The cubic root of 21206406 is about 276.7933746479.

Adding to 21206406 its reverse (60460212), we get a palindrome (81666618).

It can be divided in two parts, 21206 and 406, that added together give a palindrome (21612).

The spelling of 21206406 in words is "twenty-one million, two hundred six thousand, four hundred six".