21136666 has 4 divisors (see below), whose sum is σ = 31705002. Its totient is φ = 10568332.

The previous prime is 21136663. The next prime is 21136669. The reversal of 21136666 is 66663112.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (21136663) and next prime (21136669).

It can be written as a sum of positive squares in only one way, i.e., 20439441 + 697225 = 4521^2 + 835^2 .

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is not an unprimeable number, because it can be changed into a prime (21136663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5284165 + ... + 5284168.

Almost surely, 2^21136666 is an apocalyptic number.

21136666 is a deficient number, since it is larger than the sum of its proper divisors (10568336).

21136666 is a wasteful number, since it uses less digits than its factorization.

21136666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 10568335.

The product of its digits is 7776, while the sum is 31.

The square root of 21136666 is about 4597.4629960447. The cubic root of 21136666 is about 276.4896178577.

Adding to 21136666 its reverse (66663112), we get a palindrome (87799778).

The spelling of 21136666 in words is "twenty-one million, one hundred thirty-six thousand, six hundred sixty-six".