21263209 has 12 divisors (see below), whose sum is σ = 24749172. Its totient is φ = 18191360.

The previous prime is 21263191. The next prime is 21263213. The reversal of 21263209 is 90236212.

It is a happy number.

It can be written as a sum of positive squares in 2 ways, for example, as 7683984 + 13579225 = 2772^2 + 3685^2 .

It is not a de Polignac number, because 21263209 - 2⁹ = 21262697 is a prime.

It is a super-3 number, since 3×21263209³ (a number of 23 digits) contains 333 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21263239) 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, 3112 + ... + 7225.

It is an arithmetic number, because the mean of its divisors is an integer number (2062431).

Almost surely, 2^21263209 is an apocalyptic number.

It is an amenable number.

21263209 is a deficient number, since it is larger than the sum of its proper divisors (3485963).

21263209 is a wasteful number, since it uses less digits than its factorization.

21263209 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10376 (or 10365 counting only the distinct ones).

The product of its (nonzero) digits is 1296, while the sum is 25.

The square root of 21263209 is about 4611.2047232800. The cubic root of 21263209 is about 277.0402918100.

It can be divided in two parts, 2126 and 3209, that added together give a palindrome (5335).

The spelling of 21263209 in words is "twenty-one million, two hundred sixty-three thousand, two hundred nine".