21215623 has 8 divisors (see below), whose sum is σ = 24924816. Its totient is φ = 17803200.

The previous prime is 21215611. The next prime is 21215627. The reversal of 21215623 is 32651212.

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 21215623 - 2⁹ = 21215111 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21215594 and 21215603.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21215627) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74038 + ... + 74323.

It is an arithmetic number, because the mean of its divisors is an integer number (3115602).

Almost surely, 2^21215623 is an apocalyptic number.

21215623 is a deficient number, since it is larger than the sum of its proper divisors (3709193).

21215623 is a wasteful number, since it uses less digits than its factorization.

21215623 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148385.

The product of its digits is 720, while the sum is 22.

The square root of 21215623 is about 4606.0420102296. The cubic root of 21215623 is about 276.8334700010.

Adding to 21215623 its reverse (32651212), we get a palindrome (53866835).

It can be divided in two parts, 2121 and 5623, that added together give a square (7744 = 88²).

The spelling of 21215623 in words is "twenty-one million, two hundred fifteen thousand, six hundred twenty-three".