21203406 has 24 divisors (see below), whose sum is σ = 52503984. Its totient is φ = 6058080.

The previous prime is 21203383. The next prime is 21203407. The reversal of 21203406 is 60430212.

It is a happy number.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21203407) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 84015 + ... + 84266.

It is an arithmetic number, because the mean of its divisors is an integer number (2187666).

Almost surely, 2^21203406 is an apocalyptic number.

21203406 is an abundant number, since it is smaller than the sum of its proper divisors (31300578).

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

21203406 is a wasteful number, since it uses less digits than its factorization.

21203406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 168296 (or 168293 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 18.

The square root of 21203406 is about 4604.7156263987. The cubic root of 21203406 is about 276.7803216851.

Adding to 21203406 its reverse (60430212), we get a palindrome (81633618).

It can be divided in two parts, 21203 and 406, that added together give a square (21609 = 147²).

The spelling of 21203406 in words is "twenty-one million, two hundred three thousand, four hundred six".