21506321 has 8 divisors (see below), whose sum is σ = 22075680. Its totient is φ = 20940192.

The previous prime is 21506279. The next prime is 21506323. The reversal of 21506321 is 12360512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21506321 - 2⁶ = 21506257 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 21506293 and 21506302.

It is not an unprimeable number, because it can be changed into a prime (21506323) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 18485 + ... + 19613.

It is an arithmetic number, because the mean of its divisors is an integer number (2759460).

Almost surely, 2^21506321 is an apocalyptic number.

It is an amenable number.

21506321 is a deficient number, since it is larger than the sum of its proper divisors (569359).

21506321 is a wasteful number, since it uses less digits than its factorization.

21506321 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1615.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21506321 is about 4637.4908086162. The cubic root of 21506321 is about 278.0921360150.

Adding to 21506321 its reverse (12360512), we get a palindrome (33866833).

The spelling of 21506321 in words is "twenty-one million, five hundred six thousand, three hundred twenty-one".