21081986 has 4 divisors (see below), whose sum is σ = 31622982. Its totient is φ = 10540992.

The previous prime is 21081979. The next prime is 21082003. The reversal of 21081986 is 68918012.

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., 14295961 + 6786025 = 3781^2 + 2605^2 .

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, 5270495 + ... + 5270498.

Almost surely, 2^21081986 is an apocalyptic number.

21081986 is a deficient number, since it is larger than the sum of its proper divisors (10540996).

21081986 is a wasteful number, since it uses less digits than its factorization.

21081986 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10540995.

The product of its (nonzero) digits is 6912, while the sum is 35.

The square root of 21081986 is about 4591.5123870028. The cubic root of 21081986 is about 276.2509881690.

Adding to 21081986 its reverse (68918012), we get a palindrome (89999998).

The spelling of 21081986 in words is "twenty-one million, eighty-one thousand, nine hundred eighty-six".