21621218 has 4 divisors (see below), whose sum is σ = 32431830. Its totient is φ = 10810608.

The previous prime is 21621181. The next prime is 21621233. The reversal of 21621218 is 81212612.

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., 14845609 + 6775609 = 3853^2 + 2603^2 .

It is a junction number, because it is equal to n+sod(n) for n = 21621193 and 21621202.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 5405303 + ... + 5405306.

Almost surely, 2^21621218 is an apocalyptic number.

21621218 is a deficient number, since it is larger than the sum of its proper divisors (10810612).

21621218 is a wasteful number, since it uses less digits than its factorization.

21621218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10810611.

The product of its digits is 384, while the sum is 23.

The square root of 21621218 is about 4649.8621484943. The cubic root of 21621218 is about 278.5864902035.

The spelling of 21621218 in words is "twenty-one million, six hundred twenty-one thousand, two hundred eighteen".