21357218 has 4 divisors (see below), whose sum is σ = 32035830. Its totient is φ = 10678608.

The previous prime is 21357199. The next prime is 21357247. The reversal of 21357218 is 81275312.

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., 20912329 + 444889 = 4573^2 + 667^2 .

It is a super-2 number, since 2×21357218² = 912261521399048, which contains 22 as substring.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5339303 + ... + 5339306.

Almost surely, 2^21357218 is an apocalyptic number.

21357218 is a deficient number, since it is larger than the sum of its proper divisors (10678612).

21357218 is a wasteful number, since it uses less digits than its factorization.

21357218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10678611.

The product of its digits is 3360, while the sum is 29.

The square root of 21357218 is about 4621.3870212307. The cubic root of 21357218 is about 277.4479755299.

It can be divided in two parts, 21357 and 218, that multiplied together give a triangular number (4655826 = T₃₀₅₁).

The spelling of 21357218 in words is "twenty-one million, three hundred fifty-seven thousand, two hundred eighteen".