21136665 has 32 divisors (see below), whose sum is σ = 37604736. Its totient is φ = 10050560.

The previous prime is 21136663. The next prime is 21136669. The reversal of 21136665 is 56663112.

It is not a de Polignac number, because 21136665 - 2¹ = 21136663 is a prime.

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 in 31 ways as a sum of consecutive naturals, for example, 7537 + ... + 9953.

It is an arithmetic number, because the mean of its divisors is an integer number (1175148).

Almost surely, 2^21136665 is an apocalyptic number.

It is an amenable number.

21136665 is a deficient number, since it is larger than the sum of its proper divisors (16468071).

21136665 is a wasteful number, since it uses less digits than its factorization.

21136665 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2489.

The product of its digits is 6480, while the sum is 30.

The square root of 21136665 is about 4597.4628872890. The cubic root of 21136665 is about 276.4896134974.

Adding to 21136665 its reverse (56663112), we get a palindrome (77799777).

It can be divided in two parts, 2113 and 6665, that added together give a palindrome (8778).

The spelling of 21136665 in words is "twenty-one million, one hundred thirty-six thousand, six hundred sixty-five".