21308506 has 4 divisors (see below), whose sum is σ = 31962762. Its totient is φ = 10654252.

The previous prime is 21308477. The next prime is 21308509. The reversal of 21308506 is 60580312.

It is a happy number.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 21114025 + 194481 = 4595^2 + 441^2 .

It is not an unprimeable number, because it can be changed into a prime (21308509) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5327125 + ... + 5327128.

Almost surely, 2^21308506 is an apocalyptic number.

21308506 is a deficient number, since it is larger than the sum of its proper divisors (10654256).

21308506 is a wasteful number, since it uses less digits than its factorization.

21308506 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10654255.

The product of its (nonzero) digits is 1440, while the sum is 25.

The square root of 21308506 is about 4616.1137334342. The cubic root of 21308506 is about 277.2368785296.

Adding to 21308506 its reverse (60580312), we get a palindrome (81888818).

The spelling of 21308506 in words is "twenty-one million, three hundred eight thousand, five hundred six".