21009986 has 8 divisors (see below), whose sum is σ = 32031804. Its totient is φ = 10332720.

The previous prime is 21009983. The next prime is 21009997. The reversal of 21009986 is 68990012.

It can be written as a sum of positive squares in 2 ways, for example, as 20475625 + 534361 = 4525^2 + 731^2 .

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

It is not an unprimeable number, because it can be changed into a prime (21009983) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 85985 + ... + 86228.

Almost surely, 2^21009986 is an apocalyptic number.

21009986 is a deficient number, since it is larger than the sum of its proper divisors (11021818).

21009986 is a wasteful number, since it uses less digits than its factorization.

21009986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 172276.

The product of its (nonzero) digits is 7776, while the sum is 35.

The square root of 21009986 is about 4583.6651273844. The cubic root of 21009986 is about 275.9361418460.

Adding to 21009986 its reverse (68990012), we get a palindrome (89999998).

The spelling of 21009986 in words is "twenty-one million, nine thousand, nine hundred eighty-six".