21137986 has 4 divisors (see below), whose sum is σ = 31706982. Its totient is φ = 10568992.

The previous prime is 21137981. The next prime is 21137999. The reversal of 21137986 is 68973112.

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., 13950225 + 7187761 = 3735^2 + 2681^2 .

It is not an unprimeable number, because it can be changed into a prime (21137981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5284495 + ... + 5284498.

Almost surely, 2^21137986 is an apocalyptic number.

21137986 is a deficient number, since it is larger than the sum of its proper divisors (10568996).

21137986 is a wasteful number, since it uses less digits than its factorization.

21137986 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10568995.

The product of its digits is 18144, while the sum is 37.

The square root of 21137986 is about 4597.6065512395. The cubic root of 21137986 is about 276.4953733964.

The spelling of 21137986 in words is "twenty-one million, one hundred thirty-seven thousand, nine hundred eighty-six".