21209356 has 18 divisors (see below), whose sum is σ = 43176588. Its totient is φ = 9089640.

The previous prime is 21209327. The next prime is 21209359. The reversal of 21209356 is 65390212.

It is a Harshad number since it is a multiple of its sum of digits (28).

It is not an unprimeable number, because it can be changed into a prime (21209359) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 53910 + ... + 54301.

Almost surely, 2^21209356 is an apocalyptic number.

It is an amenable number.

21209356 is an abundant number, since it is smaller than the sum of its proper divisors (21967232).

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

21209356 is a wasteful number, since it uses less digits than its factorization.

21209356 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 108229 (or 108220 counting only the distinct ones).

The product of its (nonzero) digits is 3240, while the sum is 28.

The square root of 21209356 is about 4605.3616578940. The cubic root of 21209356 is about 276.8062088609.

Adding to 21209356 its reverse (65390212), we get a palindrome (86599568).

It can be divided in two parts, 2120 and 9356, that added together give a triangular number (11476 = T₁₅₁).

The spelling of 21209356 in words is "twenty-one million, two hundred nine thousand, three hundred fifty-six".