21420818 has 4 divisors (see below), whose sum is σ = 32131230. Its totient is φ = 10710408.

The previous prime is 21420811. The next prime is 21420827. The reversal of 21420818 is 81802412.

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., 16785409 + 4635409 = 4097^2 + 2153^2 .

It is not an unprimeable number, because it can be changed into a prime (21420811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5355203 + ... + 5355206.

Almost surely, 2^21420818 is an apocalyptic number.

21420818 is a deficient number, since it is larger than the sum of its proper divisors (10710412).

21420818 is a wasteful number, since it uses less digits than its factorization.

21420818 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10710411.

The product of its (nonzero) digits is 1024, while the sum is 26.

The square root of 21420818 is about 4628.2629570931. The cubic root of 21420818 is about 277.7231081863.

The spelling of 21420818 in words is "twenty-one million, four hundred twenty thousand, eight hundred eighteen".